Automated file error classification and correction in a hierarchical storage management system

Disclosed is a system to diagnose and handle errors in an automated hierarchical storage management system. A host system requests an access operation on a first file, such as a logical volume, in a first storage device, such as a magnetic hard disk drive. A server processes the host request to determine whether the first file is resident in the first storage device. The server initiates a recall of a second file, such as a physical volume, in a second storage device, such as tape cartridges, optical disks, etc., corresponding to the first file upon determining that the first file is not resident in the first storage device. The second file is then copied from the second storage device to the first file in the first storage device upon determining that the second file is accessible. The server further determines whether the recall of the second file has failed. Upon determining that the recall has failed, the server checks a table in a memory within the server to determine whether there is error information listed for the second file involved in the failed recall. The server then takes appropriate action based on the error information in the table.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a system for error classification and 
error handling in a hierarchical storage management system. 
2. Description of the Related Art 
Computer users today require ever increasing amounts of data storage to run 
complex applications, such as those involving digital imaging, multimedia, 
and video-on demand. These applications require massive amounts of data 
space to store files. Storage systems for non-volatile, long term storage 
of digital data include, magnetic tapes, magnetic hard disk drives, 
optical disks, holographic storage, etc. As the cost of magnetic hard disk 
drive space decreases, one solution is to use magnetic hard disk drives 
for long term data storage. Magnetic hard disk drives are preferred as 
they provide higher data transfer and access rates than other storage 
devices, such as magnetic tape cartridges, optical disks, etc. 
Notwithstanding, there are many administrative labor costs associated with 
installing, configuring and managing hard disk drives. Furthermore, a 
large amount of data residing on hard drives is inactive. In fact, it is 
estimated that only twenty percent of information stored on a network is 
accessed during the course of a month. One solution is to store more 
frequently used data on hard disk drives and periodically back-up less 
frequently used data to magnetic tape such that the more frequently used 
data is resident on the hard disk drives. Such a system takes advantage of 
the low cost of tape drives and tape media to archive less frequently used 
data and at the same time maintain more frequently used data available on 
the faster, yet costlier, hard disk drives. Maintaining less frequently 
used data on slower hard disk drives will likely have a negligible effect 
on system users. The benefits of providing a primary storage of hard disk 
drives and a secondary storage comprised of a less expensive, and 
typically slower media, is further discussed in "ADSTAR Distributed 
Manager (ADSM)--Hierarchical Storage Management (HSM) White Paper (IBM 
Document No. G522-24322-00, International Business Machines, 1996), which 
is incorporate herein by reference in its entirety. 
International Business Machines Corporation (IBM) developed the ADSTAR 
Distributed Storage Manager (ADSM) to provide hierarchical storage 
management (HSM) over data storage devices. The concept of HSM is to 
transparently migrate infrequently accessed data automatically from more 
costly, higher performance storage devices, such as hard disk drives, to 
less expensive, slower storage devices such as tape drives and optical 
libraries. In the ADSM system, when a primary storage device, such as a 
hard disk drive directly accessible to users, reaches a predetermined 
threshold, the least frequently used files are migrated to tape storage. 
The migrated files on the hard disk drive are replaced with a small stub 
file identifying the location of the migrated file on the tape drive. The 
stub file would present information on the file name and other 
characteristics to system users browsing the hard disk drive. Thus, to 
system users, the stub file appears to be the complete migrated file. When 
a system user accesses the stub file, the ADSM would recall the file 
represented by the stub file from the tape archive and copy it to the 
local hard drive to make the data available to system users. In this way, 
tape storage provides seamless and unlimited disk space which is 
accessible at all times to system users as if the data was always resident 
on the local hard disk drive. 
Various system errors may arise when a server attempts to transfer data 
between secondary storage, such as a tape cartridge, and primary storage, 
such as a local hard disk drive. In many prior art systems, the server 
provides only limited information on the access error. For instance, the 
IBM AIX version for ADSM provides only minimal error information in the 
form of the ENOTREADY error code. The ENOTREADY code indicates that the 
tape system was not ready for operation or the tape was not loaded in the 
drive. Moreover, in prior art systems, if an error occurs when a tape 
drive is accessed during operations, the user must contact a human system 
administrator to diagnose and handle the error. 
SUMMARY OF THE INVENTION 
To overcome the limitations in the prior art described above, the present 
invention discloses a system to diagnose and handle an error in an 
automated hierarchical storage management system. A host system requests 
an access operation on a first file in a first storage device. A server 
processes the host request to determine whether the first file is resident 
in the first storage device. The server initiates a recall of a second 
file in a second storage device corresponding to the first file upon 
determining that the first file is not resident in the first storage 
device. The second file is then copied from the second storage device to 
the first file in the first storage device upon determining that the 
second file is accessible. The server further determines whether the 
recall of the second file in the second storage device has failed. If the 
recall fails, the server checks a table in a memory within the server to 
determine whether there is error information listed for the second file 
involved in the failed recall. The server then takes appropriate action 
based on the error information in the table. 
In further embodiments, the first file is a logical volume observable to 
the host system and the second file is a physical volume in the second 
storage device that corresponds to the logical volume. 
In still further embodiments, the first storage device is a magnetic hard 
disk drive and the second storage device is a member of the set of storage 
devices comprising magnetic tape cartridges, optical disks, holographic 
storage units, and magnetic hard disk drives. 
It is an object of the present invention to provide detailed error 
information and error classification on file errors in a secondary storage 
device which provides back-up and archival storage for files in a primary 
storage device. 
It is a further object to initiate error handling and recovery operations 
for files in the secondary storage device based on the detailed error 
information.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the following description, reference is made to the accompanying 
drawings which form a part hereof, and which is shown, by way of 
illustration, several embodiments of the present invention. It is 
understood that other embodiments may be utilized and structural changes 
may be made without departing from the scope of the present invention. 
Hardware and Software Environment 
FIG. 1 is a block diagram of a preferred embodiment of a distributed 
computer system 2 in accordance with the present invention. A host system 
4 is linked to a virtual tape server 6 via a network connection (e.g., 
TCP/IP, LAN, Ethernet, the IBM Enterprise System Connection (ESCON), 
etc.). In preferred embodiments, the host system 4 is a computer, such as 
a personal computer, workstation, mainframe, etc. that is linked to the 
virtual tape server 6 via an ESCON channel. The host system 4 operates 
under control of an operating system such as MVS, AIX, Windows, etc. The 
virtual tape server 6 is a computer such as a personal computer, 
workstation or mainframe which operates under control of an operating 
system (OS) 7, such as the IBM Corporation AIX, MVS, VM or OS/390 
operating system, or other operating systems such as Windows, UNIX, etc. 
The virtual tape server 6 is associated with a Direct Access Storage 
Device (DASD) cache 8. In preferred embodiments, the DASD cache 8 is 
comprised of a plurality of hard disk drives which are configured into one 
or more RAID arrays. The arrangement and organization of hard disk space 
into RAID arrays is described in Peter M. Chen, Edward K. Lee, Garth A. 
Gibson, Randy H. Katz, and David A. Patterson, "RAID: High-Performance, 
Reliable Secondary Storage," ACM Computing Surveys, Vol. 26, No. 2, June 
1994, which is incorporated herein by reference in its entirety. 
A tape library 10 includes a plurality of tape drives (TDs), such as the 
IBM Magstar 3590 tape drives. In the preferred embodiment of FIG. 1, the 
tape library 10 includes three to six tape drives (TDs). A tape cartridge 
is loaded into each tape drive (TDs). The tape library 10 could include 
hundreds of such cartridges. All host interaction with the tape library 10 
is through the virtual tape server 6. The tape library 10 can load and 
eject tape cartridges using a robotic arm, and clean the tape drives. 
Further, the tape library 10 may include storage management software to 
monitor the active space on the tape cartridges and schedule reclamations 
of tape cartridges when the system is less active. In preferred 
embodiments, the tape library 10 may be comprised of a tape library such 
as the IBM Magstar 3494 Tape Library. A library manager 12 has the ability 
to install, maintain, configure, and operate the tape library 10. The 
library manager 12 consists of a controller (a personal computer, 
workstation, etc.) which can assume direct control over the tape library 
10. 
The DASD cache 8 provides a cache for data stored in the tape library 10. 
The DASD cache 8 maintains logical volumes as logical volume files which 
are concatenated into physical volume files in the tape cartridges loaded 
in the tape drives (TDs). When a logical volume file in the DASD cache 8 
moves to a tape drive (TD) in the tape library 10, the logical volume file 
is written to a physical volume file in the actual tape drive (TD). When a 
physical volume file is recalled from a tape drive (TD) and moved to the 
DASD cache 8 it then becomes a logical volume file in the DASD cache 8. In 
this way, the DASD cache 8 provides a window to the host system 4 of all 
physical volumes in the tape library 10. In preferred embodiments, the 
logical volume files comprise 250 Mb to 800 Mb of storage space. The size 
of the logical volume file may be reduced to minimize the time needed to 
transfer a volume from the tape library 10 to the DASD cache 8 or, 
alternatively, increased in size as the size of hard disk drives and tape 
cartridge transfer speeds increase. 
Upon initialization, the virtual tape server 6 loads a virtual tape 
controller 14 into random access memory (RAM). The virtual tape controller 
14 is comprised of a plurality of virtual tape daemons 15.sub.i which 
represent and emulate to the host system virtual tape devices. In the 
preferred embodiment, n equals thirty two, which means that there are 
thirty-two virtual tape daemons 15.sub.0 to 15.sub.31 and, likewise, 
thirty-two virtual tape devices. The host system 4 operating system 
manages the presentation of virtual tape devices to system users. The host 
system 4 views the virtual tape devices as actual tape drives. When the 
host system 4 attempts to access a logical volume in a selected virtual 
tape device, the virtual tape daemon 15.sub.i for the virtual tape device 
requested by the host system 4 would handle the host access request. For 
instance, if the host system 4 requests to access virtual tape device 4, 
virtual tape daemon 15.sub.3 in the virtual tape controller 14 would 
handle the host 4 request. The virtual tape daemons 15.sub.0 to 15.sub.n 
cooperate with the kernel of the operating system 7 to intercept requests 
by the host system 4 to access a logical volume in a virtual tape device 
in the DASD cache 8. 
A hierarchical storage management (HSM) client program 16 intercepts and 
processes the access request from the virtual tape daemons (15.sub.0 to 
15.sub.n). The HSM client 16 then carries out the host system 4 request to 
access the logical volume file on the DASD cache 8. In preferred 
embodiments, the HSM client program 16 is part of the IBM ADSTAR 
Distributed Storage Manager (ADSM) product, which is described in "ADSM 
Version 2 Presentation Guide," (IBM Document SG24-4532-00, International 
Business Machines, copyright 1995). ADSM provides generic client/server 
HSM functions. The ADSM product includes an ADSM client to handle file 
access requests with software integrated with the operating system kernel. 
A storage manager server program 18 handles data transfers between the DASD 
cache 8 and the tape library 10. For instance, if the HSM client 16 
attempts to mount a logical volume file which is not located on the DASD 
cache 8, then the HSM client 16 will communicate the access request to the 
storage manager server 18. If the tape in the access request is mounted in 
a tape drive (TD) in the tape library 10, then the storage manager server 
18 will access the physical volume for the requested logical volume file 
from the mounted tape. However, if the requested file is on a tape not 
presently mounted in a tape drive (TD), then the storage manager server 18 
will request the library manager 12 to mount the tape containing the 
physical volume corresponding to the requested logical volume file. In 
preferred embodiments, the storage manager server 18 program is part of 
the IBM ADSM product. The ADSM product includes the ADSM server to manage 
transfer of files from a client, which in FIG. 1 is the HSM client 16, to 
a storage area, which in FIG. 1 is the tape library 10. In preferred 
embodiments the HSM client 16 and storage manager server 18 are on the 
same machine, i.e., the virtual tape server 6. In such case, the HSM 
client 16 and storage manager server 18 utilize the memory of the virtual 
tape server 6 to transfer data and control information therebetween. ADSM 
provides its shared memory protocol for communication between the HSM 
client 16 and storage manager server 18 on the same machine. In 
alternative embodiments, the virtual tape server 6 may be distributed 
across multiple computers. In such case, the storage manager server and 
HSM client 16 may be on different computer platforms and communicate via a 
network protocol such as TCP/IP, IPX/SPX, etc. 
In preferred embodiments, the storage manager server 18 migrates entire 
logical volume files from the DASD cache 8 to the tape library 10. When 
the available space in the DASD cache 8 reaches a predetermined level, the 
HSM client 16 will direct the storage manager server 18 to migrate logical 
volume files from the DASD cache 8 to the tape library 10 for archival 
therein. The HSM client 16 will substitute the migrated logical volume 
file with a stub file which includes all the information needed to locate 
and recall a physical volume file from the tape library 10 that 
corresponds to the logical volume file represented by the stub file. Thus, 
the stub file would appear to a host system 4 as a logical volume. 
However, when the HSM client 16 attempts to access a stub file, the HSM 
client would have the storage manager server 18 recall the logical volume 
file from the physical volume in the tape library 10 to replace the stub 
file in the DASD cache 8. Typically, the HSM client 16 would migrate the 
least used logical volume files. 
An automated systems administrator 20 program included in the virtual tape 
server 6 performs operations typically performed by a human systems 
administrator. The automated systems administrator 20 filters any error 
messages concerning the tape library 10 that are generated by the storage 
manager server 18. The storage manager server 18 receives error 
information updates from the library manager 12. The automated systems 
administrator 20 stores information associated with physical volumes in an 
associated volume status table 22. In preferred embodiments, the volume 
status table 22 is maintained in a memory structure accessible to the 
automated systems administrator program 20. The volume status table 22 
includes a minimum of two columns of information. The first column 
identifies the physical volume of a tape cartridge, including its serial 
number and/or tape identification number, and the second column includes 
an entry describing a particular problem with the tape cartridge or 
physical volume identified in the first column. 
A premigration table 24 is a further memory structure accessible to the 
automated systems administrator 20. The premigration table 24 maintains 
information on any logical volume files that are in the process of being 
premigrated from the DASD cache 8 to the tape library 10. During 
premigration, a logical volume file is locked while the storage manager 
server 18 copies data from the logical volume file in the DASD cache 8 to 
the tape library 10. While the storage manager server 18 is copying a 
logical volume file from the DASD cache 8 to the tape library 10, the file 
name is placed in the premigration table 24 to indicate that the logical 
volume file is presently in the process of being premigrated. Once the 
logical volume file is copied over to the tape library 10, the logical 
volume file name is removed from the premigration table 24. At this point, 
the logical volume file is maintained in both the DASD cache 8 and the 
tape library 10. When the available space in the DASD cache 8 reaches a 
predetermined low threshold, the logical volume files that have been 
premigrated, such that a copy is maintained in both the DASD cache 8 and 
the tape library, are deleted from the DASD cache 8 and replaced with a 
stub file. This process of deleting the logical volume files from the DASD 
cache 8 and replacing the moved files with a stub file is referred to 
herein as migration. 
In preferred embodiments, the automated systems administrator program 20 
determines when the storage manager server 18 should premigrate and 
migrate files from the DASD cache 8 to the tape library 10. In such case, 
the automated systems administrator program 20 would update the 
premigration table 24 with those files in the DASD cache 8 that are in the 
process of being premigrated. Moreover, the automated systems 
administrator 20 provides error information to the library manager 12. 
FIG. 2 is a block diagram providing further details on the software 
components within the system administration program 20, the storage 
manager server 18, and the virtual tape daemons 15.sub.0 -15.sub.n, and 
the interaction therebetween. The automated systems administrator program 
20 can transmit commands to the storage manager server 18 to control tape 
library 10 access operations via a command interface 26 thread in the 
storage manager server 18. For instance, the automated systems 
administrator 20 could cause the storage manager server 18 to migrate 
logical volumes files from the DASD cache 8 to the tape library 10 by 
issuing such a command to the command interface 26 thread of the storage 
manager server 18. The automated systems administrator 20 includes a 
Console Parser 28 thread which receives input from a console output 30 of 
the storage manager server 18. The console output 30 pipes all storage 
manager server 18 error messages to the Console Parser 28, which then 
sends the parsed messages to a Console Handler 32 thread. The Console 
Handler 32 thread determines whether the error message is relevant to the 
operation of the tape library 10. If the error message is relevant, then 
the Console Handler 32 updates the volume status table 22 with the error 
information. As discussed, the error information maintained in the volume 
status table 22 is maintained on a physical volume file basis. The 
automated systems administrator 20 can provide error messages to the 
library manager 12 which were provided to one of the virtual tape daemons 
15.sub.0 to 15.sub.n. 
A virtual tape daemon 15.sub.i may receive an error message from the HSM 
client 16 without any indication of the nature of the error. To further 
diagnose the error, the virtual tape daemon 15.sub.i would call an Error 
Query 34.sub.i function, shown in FIG. 2, to diagnose the error and take 
any appropriate action. The Error Query 34.sub.i function takes as 
parameters the logical volume file name where the error occurred and the 
error type. For instance, in the IBM AIX operating system, a typical error 
message is ENOTREADY, which indicates that a tape drive (TD) within the 
tape library 10 was not ready for operation or a tape cartridge is not 
mounted in the tape drive (TD). The Error Query 34.sub.i function builds a 
request, which is then transferred via a Request Queue 36 to an Error 
Query Handler 38 thread in the automated systems administrator 20. The 
Error Query Handler 38 thread processes the request and returns a response 
to the appropriate Error Query 34.sub.i function via a Response Queue 40. 
Numerous Error Query 34.sub.i functions could be called simultaneously. 
For instance, virtual tape daemons 15.sub.0 -15.sub.n could all call and 
execute their respective Error Query 34.sub.0 -34.sub.n functions 
simultaneously. 
Error Classification and Handling 
FIGS. 3a and 3b are flowcharts illustrating preferred embodiments of the 
logic for handling an error when a host 4 attempts to access a file in the 
tape library 10. This logic is implemented in the software and hardware 
components of the host 4, virtual tape server 6, tape library 10, and 
library manager 12. Those skilled in the art will recognize that this 
logic is provided for illustrative purposes only and that different logic 
may be used to accomplish the same results. 
Control begins at block 50 which represents the host system 4 attempting to 
access a logical volume in a virtual tape device, which is linked by a 
corresponding virtual tape daemon 15.sub.i to the requested logical volume 
file in the DASD cache 8. Logical volume files have corresponding physical 
volume files in the tape library 10. Examples of file access operations 
include open, read, and write operations. Control transfers to block 52 
which represents the host 4 requesting the virtual tape server 6 to mount 
the virtual tape device with a logical volume. Control transfers to block 
54 which represents the appropriate virtual tape daemon 15.sub.i 
processing the request to mount the logical volume from the host 4. At 
block 56, the virtual tape daemon 15.sub.i generates a request to mount 
the logical volume file requested by the host 4. Control transfers to 
block 58 which represents the HSM client 16 processing the request from 
the virtual tape daemon 15.sub.i to open the logical volume file. At block 
60, the HSM client 16 checks if the logical volume file is resident in the 
DASD cache 8. Control transfers to block 62 which is a decision block 
representing the HSM client 16 determining whether the targeted logical 
volume file is loaded in the DASD cache 8. If so, control transfers to 
block 64; otherwise control transfers to block 66. 
Block 64 represents the HSM client 16 notifying the requesting virtual tape 
daemon 15.sub.i that the logical volume file is mounted in the DASD cache 
8. The virtual tape daemon 15.sub.i then notifies the host system 4 that 
the logical volume is mounted and that that file access request(s) for the 
files located in the mounted logical volume can be serviced. If the 
logical volume file is not resident in the DASD cache 8, then control 
transfers to block 66, which represents the HSM client 16 requesting the 
storage manager server 18 to recall the logical volume file from the 
corresponding physical volume on a tape drive (TD) in the tape library 10. 
Control then transfers to block 68 which represents the storage manager 
server 18 failing in its attempt to recall the logical volume file from 
the physical volume file in the tape library 10. As discussed, in 
preferred embodiments, the storage manager server 18 can access tapes 
directly in the tape library 10. However, if a tape is not mounted, the 
storage manager server 18 must request the library manager 12 to mount the 
tape. Typically, the error message provided from the library manager 12 to 
the storage manager server 18 will only indicate that an error has 
occurred without indicating the type of error, e.g., ENOTREADY. The HSM 
client 16 passes this error message to the requesting virtual tape daemon 
15i. Upon receiving the generic error message, at block 70, the requesting 
virtual tape daemon 15.sub.i calls the Error Query 34.sub.i function. The 
called Error Query 34.sub.i function receives the name of the logical 
volume file which failed to mount and the error message, and based thereon 
builds a request for error information which is transmitted to the Error 
Query Handler 40 in the automated systems administrator 20 via the Request 
Queue 36. 
Control transfers to block 72, which represents the Error Query Handler 40 
thread processing the request from the called Error Query 34.sub.i 
function in virtual tape daemon 14.sub.i. Control transfers to block 74 
which represents the Error Query Handler 40 checking the premigration 
table 24. At block 76, the Error Query Handler 40 determines whether the 
requested logical volume file is in the premigration table 24, thereby 
indicating that the requested logical volume file is presently being 
premigrated to the tape library 10. If so, control transfers to block 78; 
otherwise, control transfers to block 80. Block 78 represents the Error 
Query Handler 40 notifying the Error Query 34 thread via the Response 
Query 38 to retry mounting the logical volume file after determining that 
the automated systems administrator 20 has now removed the logical volume 
file name from the premigration table 24. As discussed, after 
premigration, the logical volume file is resident in both the DASD cache 8 
and the tape library 10. 
Block 80 is a decision block representing the error query handler 40 
determining whether the requested logical volume file is resident in the 
DASD cache 8. If so, control transfers to block 82; otherwise control 
transfers to block 84. Block 82 represents the Error Query Handler 40 
notifying the Error Query 34.sub.i function via the Response Queue 38 to 
retry mounting the logical volume file as the logical volume file is not 
in the premigration table and is resident in the DASD cache 8. Block 84 is 
shown in FIG. 3b and represents the automated systems administrator 20 
requesting the storage manager server 18 via the command interface 26 for 
the physical volume file address of the logical volume file at which the 
error occurred. Control transfers to block 86 which represents the Error 
Query Handler 40 thread checking the volume status table 22 for error 
information for the physical volume file provided by the storage manager 
server 18 where the error occurred. Control then transfers to block 88 
which represents the Error Query Handler 40 determining whether the error 
in the volume status table 22 for the physical volume file is a permanent 
read error. If so, control transfers to block 90; otherwise, control 
transfers to block 92. 
If the error for the physical volume file in the volume status table 22 is 
a permanent read error, then, at block 90, the Error Query Handler 40 
requests the automated systems administrator 20 to initiate the recovery 
process. Control transfers to block 94 which represents the automated 
systems administrator 20 moving the stub file (F.sub.0) that references 
the physical volume with the read error to a new file name (F.sub.1) on 
the DASD cache 8. Control transfers to block 96 which represents the HSM 
client 16 recalling the stub file (F.sub.1) and requesting the storage 
manager server 18 to recover data from the physical volume referenced by 
the stub file (F.sub.1) by copying data from the physical volume to a file 
with the original file name (F.sub.0) on the DASD cache 8 until the 
damaged portion of the physical volume file is reached. After copying as 
much data as possible from the front end of the physical volume file to 
the file (F.sub.0) in the DASD cache 8, the error recovery process is 
terminated. At the completion of error recovery, the recovered data is 
maintained in the file name (F.sub.0) and the original contents for the 
stub file (F.sub.0) are maintained in stub file (F.sub.1). The stub file 
is maintained because the entire logical volume file was not successfully 
mounted from the tapes. The Error Query Handler 40 is notified of the 
termination of the error recovery process. Control then transfers to block 
98 which represents the Error Query Handler 40 notifying the Error Query 
34.sub.i function to retry accessing the logical volume file in the DASD 
cache 8. In alternative embodiments, during the read recovery process, the 
storage manager server 18 may copy all data on the tape cartridge in the 
tape drive (TD) prior to the damaged portion of the tape, then skip the 
damaged portion of the tape cartridge, and then proceed to copy data 
following the damaged portion. Other alternative methods for recovering 
data known by those skilled in the art could also be employed to recover 
as much data as possible from the tape drive (TD) where the permanent read 
error is located, including the use of error correction codes (ECC). 
If the error in the volume status table 22 for the physical volume is not a 
permanent read error, control transfers to block 92 which represents the 
Error Query Handler 40 identifying a different error type in the volume 
status table 22. Control then transfers to block 100, which represents the 
Error Query Handler 40 generating and transmitting an appropriate response 
to the Error Query 34.sub.i function via the Response Query 38 based on 
the error located in the volume status table 22. The Error Query Handler 
40 may indicate to the Error Query 34.sub.i function an appropriate action 
for the error listed in the volume status table 22, such as to retry 
mounting the logical volume or give-up. After the error is handled, 
control transfers to block 102 which represents the automated systems 
administrator 20 sending an error notification message to the library 
manager 12. 
For instance, if the volume status table 22 indicates that the targeted 
physical volume file is on a tape cartridge that is missing, then the 
Error Query Handler 40 would notify the Error Query 34.sub.i function to 
give up attempting to mount the missing tape cartridge and provide a 
message to the library manager 12 that the recall of a physical volume 
file has failed because the tape cartridge containing the physical volume 
file is missing. In further embodiments, the Error Query 34.sub.i function 
may receive the retry response from the Error Query Handler 40 several 
times if the same error reoccurs. In such case, the Error Query 34.sub.i 
function would give-up attempting to mount the logical volume file after 
failing a predetermined number of retries. 
In this way, preferred embodiments of the present invention provide logical 
to physical error mapping, and a system for automated and intelligent 
error classification, error handling, and retry control. 
CONCLUSION 
This concludes the description of the preferred embodiments of the 
invention. The following describes some alternative embodiments for 
accomplishing the present invention. 
Preferred embodiments were described with respect to a software arrangement 
in the virtual tape server comprising various threads and objects. Those 
skilled in the art will appreciate that an alternative software structure 
comprised of alternative threads and objects could be utilized. Still 
further, the preferred embodiment described the virtual tape server and 
the software components thereof as being implemented in a single computer. 
However, in alternative embodiments, the functions performed by the 
virtual tape server 6 and software components thereof could be distributed 
across multiple computer platforms. 
In the preferred embodiment, the DASD cache 8 is comprised of magnetic hard 
disk drives. In alternative embodiments, the DASD cache 8 could be 
comprised of any suitable non-volatile memory storage device known in the 
art. Still further, the tape library 10 is described as comprised of 
magnetic tape cartridges. However, in alternative embodiments, the tape 
library 10 may be comprised of magnetic hard disk drives, optical disks, 
holographic storage units, and any other non-volatile storage medium known 
in the art that is suitable for archival and backup purposes. 
Preferred embodiments are described with respect to logical and physical 
volumes stored as single files having a size of 250 Mb to 800 Mb. However, 
in alternative embodiments, the logical and physical volumes may be stored 
as groups of files having various sizes or as a single file having a size 
different from the sizes discussed above. 
In summary, preferred embodiments in accordance with the present invention 
provide a system to diagnose and handle errors in an automated 
hierarchical storage management system. A host system requests an access 
operation on a first file in a first storage device. A server processes 
the host request to determine whether the first file is resident in the 
first storage device. The server initiates a recall of a second file in a 
second storage device corresponding to the first file upon determining 
that the first file is not resident in the first storage device. The 
second file is then copied from the second storage device to the first 
file in the first storage device upon determining that the second file is 
accessible. The server further determines whether the recall of the second 
file in the second storage device has failed. If the recall fails, the 
server checks a table in memory within the server to determine whether 
there is error information listed for the second file involved in the 
failed recall. The server then takes appropriate action based on the error 
information in the table. 
The foregoing description of the preferred embodiments of the invention has 
been presented for the purposes of illustration and description. It is not 
intended to be exhaustive or to limit the invention to the precise form 
disclosed. Many modifications and variations are possible in light of the 
above teaching. It is intended that the scope of the invention be limited 
not by this detailed description, but rather by the claims appended 
hereto. The above specification, examples and data provide a complete 
description of the manufacture and use of the composition of the 
invention. Since many embodiments of the invention can be made without 
departing from the spirit and scope of the invention, the invention 
resides in the claims hereinafter appended.