From: MICHAEL.WILLETT@OFFICE.WANG.COM ("Michael Willett")
Newsgroups: comp.sys.sgi
Subject: Re: RAID 7 systems for SGI workstations versus earlier RAID 5
Date: 1 Oct 92 05:17:00 GMT
Organization: Mail to News Gateway at Wang Labs

Regarding the questions and comments about RAID 7 for SGI versus the earlier
RAID 4 and 5, all I know is what I read from the Storage Computer RAID 7
brochure which reads as follows:

"Question. I am confused.  For transaction processing, how can a RAID 7
deliver higher performance than the operation of a RAID 5?"

"Answer. One reason mentioned earlier is that RAID 7 will always have a
higher average number of concurrent events being processed than a RAID 5
with the same number of drives.  Another reason is a basic flaw in the
RAID 5 architecture.  By rotating parity and interleaving these parity
sectors or blocks with the data, RAID 5 increases the average data
access time for every read and write, because it has to seek across more
cylinders for the same data.  If a RAID 7 has a data access time equal to
1, then a RAID 5 with the exact same drive will need 1+(1/N) time.  Granted
that this penalty declines with more drives in the array, but it never goes
away.  RAID 5 will always have to seek data across more cylinders; that
always takes more time, and therefore RAID 5 will always be slower than a
basic RAID 7.  Also the StorComp Operating System speeds up transaction
processing by the sophisticated management of the Principle of Locality."

Generally speaking, it would seem to be important to have the key RAID 7
executives themselves provide detailed information on such RAID 7 questions
via the network, so we can get the full story.  It would be interesting if
we could get long term RAID 7 SGI strategy information from them also.

As far as questions about Japanese investment in the firm go, I have zero
information on this topic.  Logical candidates would seem to be Fujitsu,
Hitachi, and Toshiba, I suppose.  Currently, the firm is private so it is
not possible to buy shares on the US or Japanese exchanges.
--------------------------------

Regarding John Scoggin's request for information on RAID systems for
VINES, Storage Computer of Nashua, N.H. is currently showing its new high
performance SCSI-RAID 7 disk array platforms at the September Banyan Users
Meeting.  They work equally well with NetWare, IBM systems, workstations
like SGI's and the RS/6000, the VAX, etc.

Standards-based, RAID 7 is designed for enterprise-wide computing and
overcomes performance limitations of earlier RAID architectures, providing
a  "real world sustained application performance improvement of 200% to
400%" and dropping the cost of storage to 16 cents/MB.  Their brochures
say they can "mix and match" up to 48 SCSI commodity (3.5 or 5.25 inch)
drives, up to 150 GB.  The RAID 7 disk array platforms come with an embedded
operating system and up to 12 SCSI-2 based host interfaces.  Besides servers,
Storage Computer's RAID 7 disk array platforms can connect to workstations
and midrange systems in addition to IBM's.  Multiple CPUs can be attached to
same disk array platform.

The RAID 7 platforms come with up to 256 MB of cache, eliminating any
reason for using performance-damaging CPU main memory disk RAM.

The drives are "hot plugable" for uninterrupted, transparent operation,
with a hot standby drive automatically replacing a failed drive.

There was a lot of activity yesterday at the Storage Computer RAID 7 booth
at the Banyan show as I walked by.  They were demoing what happens if a
drive goes down, showing the backup drive taking over.

For further information on Storage Computer's RAID 7 for various systems, the
key contact is indicated to be John O'Brien, Director of Technical Services,
at Tel. 603-880-3005 or FAX 603-889-7232.  He's the "guru" of RAID 7 and
a leading RAID industry figure.  He has a lot of published articles on the
topic and you might ask them for copies.

Michael.Willett@OFFICE.Wang.com