From: olson@anchor.esd.sgi.com (Dave Olson)
Subject: Re: Formatting 2 gigabyte disks (also, striping questions)
Organization:  Silicon Graphics, Inc.  Mountain View, CA
Date: Thu, 23 Jul 92 00:51:51 GMT

In <1992Jul22.213912.13138@ncsu.edu> garvin@cfd.mae.ncsu.edu (Michael Garvin) writes:


| 	I have what are probably a few senseless questions.  Our setup is a
| Power Series 4D/440 with a Jaguar differential SCSI controller.  Connected to
| each channel is a third-party drive tray containing four Micropolis 1548 disks
| (2,000 MB/unit unformatted capacity, 1,748 MB/unit formatted) and a single
| ended SCSI to differential SCSI converter.  After formatting and partitioning
| the disks I notice a few curious things.  First, fx reports, correctly I
| believe, the drive geometry:
...
| showing 2,112 cylinders which is close to what the Micropolis manual states
| (2,099 unformatted, 2089 formatted).  However, the partition table (partition
| ten in particular) tell a different story:
| 
| ----- partitions-----
| part  type       cyls             blocks          Megabytes   (base+size)
|   0: efs        3 + 16         5871 + 31312         3 + 15
|   1: rawdata   19 + 41        37183 + 80237        18 + 39
|   6: efs       60 + 1651     117420 + 3231007      57 + 1578
|   7: lvol       3 + 1708       5871 + 3342556       3 + 1632
|   8: volhdr     0 + 3             0 + 5871          0 + 3
|  10: entire     0 + 1711          0 + 3348427       0 + 1635
| 
| Is this discrepancy (2,089 vs 1711 cylinders) a possible bug in fx?  What leads

No.  The 'cylinder' numbers in the partition layout are logical cylinders,
calculated to give the maximum capacity on the drive.  You will something
similar to this with most zoned drives, because sectors/cylinder isn't
a constant.

| me to think this is that 1,711 works out close to 1.65 gigabytes, the size of
| the largest drive SGI is supporting.  I've tried altering that parameter, but
| fx refuses to let me do so.

You can use the /debug/showcapacity menu to show the actual capacity
(in sectors) of the drive.  It should be quite close to 3348427, but
somewhat greater.  Perhaps the formatted capacity you were quoted doesn't
include all the spare sectors (8*2089 + 45*131 is another 22607 sectors,
but that still doesn't bring you up to 1.748 Mbytes).  It is also possible
that they are quoting 10^6 Mbytes, instead of 2^20 Mbytes; I tend to
suspect this because 1.748 Gbytes (10^9 Gbytes) gives 3334000 sectors,
which is pretty close to what you show.

| 	Secondly, I was wondering if someone would critique my striping scheme.
| Here's my /etc/lvtab file:
| 
| -=-=-=-=-
| #
| # Logical volumes on Falcon drive trays (each with four two-gigabyte drives).
| #
| lv0:First 8 Gigabyte Striped Logical Volume:stripes=4:devs=/dev/dsk/jag0d2s7, \/dev/dsk/jag0d3s7, /dev/dsk/jag0d10s7, /dev/dsk/jag0d11s7
| 
| lv1:Second 8 Gigabyte Striped Logical Volume:stripes=4:devs=/dev/dsk/jag0d4s7, \
| /dev/dsk/jag0d5s7, /dev/dsk/jag0d12s7, /dev/dsk/jag0d13s7
| -=-=-=-=-
| 
| As I understand it this should provide maximum performance by striping across
| each of the four two-gigabyte drive (an eight gigabyte partition), with two
| drives in each logical volume being on a controller channel.  Comments?

I haven't worked with the jag controllers much, but I don't think this
is really the ideal configuration, since 2 of the drives in each lv are
likely to be idle at any given time (for sequential i/o).

Specifying a step size may help.

--
Let no one tell me that silence gives consent,  |   Dave Olson
because whoever is silent dissents.             |   Silicon Graphics, Inc.
    Maria Isabel Barreno                        |   olson@sgi.com
Newsgroups: comp.sys.sgi