Re: VMS and storage subsystems documentation ?

On Sat, 3 Mar 2007, JF Mezei wrote:
Is there a VMS manual that describes how VMS interfaces with various storage subsystems ?

The best document I've seen is chapter 7 of the "Guidelines for OpenVMS Cluster Configurations". It's chapter 7 in the 8.3 docs anyway.

It is also unclear to me how the disk entities virtualised by storage arrays appear on VMS. Are they SCSI devices with SCSI-ID and LUN as identification for each device ? Or are they totally separate devices requiring their own special driver ?

It's not too different from a CI cluster.

In a CI cluster, the VAX plugs into the starcoupler which plugs into the HSC which serves the disk.

In FC, the Alpha/Itanium box plugs into a Fiber Channel switch which plugs into a HSG/HSV which serves storage. Same idea. Different technology.

The HSV storage systems present total virtualized storage. You add physical disks to the storage cabinet to give it a pool of storage. Then you carve out virtual "disks" of any size you want. That's simplified, but the basic idea. When you create the virtual disk, you give it a VMS unit number.

Let's say you give it unit number "102", it will show up on the VMS server as disk device $1$DGA102:

Here's a sample (a shadowset, actually):

Disk DSA10:, device type Generic SCSI disk, is online, mounted, file-oriented
device, shareable, available to cluster, error logging is enabled, device
supports bitmaps (no bitmaps active).

Error count 0 Operations completed 231774878
Owner process "" Owner UIC [SYSTEM]
Owner process ID 00000000 Dev Prot S:RWPL,O:RWPL,G:R,W
Reference count 1 Default buffer size 512
Total blocks 314572800 Sectors per track 128
Total cylinders 19200 Tracks per cylinder 128
Logical Volume Size 314572800 Expansion Size Limit 2147450880

Volume label "POUR_RAID" Relative volume number 0
Cluster size 8 Transaction count 1
Free blocks 313829248 Maximum files allowed 16711679
Extend quantity 5 Mount count 4
Mount status System Cache name "_DSA1:XQPCACHE"
Extent cache size 64 Maximum blocks in extent cache 31382924
File ID cache size 64 Blocks in extent cache 21733648
Quota cache size 0 Maximum buffers in FCP cache 5083
Volume owner UIC [SYSTEM] Vol Prot S:RWCD,O:RWCD,G:RWCD,W:RWCD

Volume Status: ODS-2, subject to mount verification, write-back caching
enabled.
Volume is also mounted on BARNEY, FRED, MACK.

Disk $1$DGA3305:, device type HSV110, is online, device has multiple I/O paths,
member of shadow set DSA10:, error logging is enabled.

Error count 0 Shadow member operation count 238844112
Current preferred CPU Id 3 Fastpath 1
WWID 01000010:6005-08B4-0010-491D-0000-6000-0087-0000
Allocation class 1

I/O paths to device 4
Path PGA0.5000-1FE1-5006-6C7D (ROCK), primary path.
Error count 0 Operations completed 3275
Path PGA0.5000-1FE1-5006-6C78 (ROCK).
Error count 0 Operations completed 3272
Path PGB0.5000-1FE1-5006-6C7C (ROCK).
Error count 0 Operations completed 3273
Path PGB0.5000-1FE1-5006-6C79 (ROCK), current path.
Error count 0 Operations completed 238834292


The best part is how it works with dynamic volume expansion. Since the DGA device is completely virtual, you can change the size of the device at the HSV on-the-fly. This virtual device is about 150GB. Not enough, space? I go to the HSV and say "make it 250GB". Assuming I have enough free storage pool, it will do that.

Then on the VMS side, I say SET VOL/LIMIT and the size changes.

This works assuming you did an INIT/LIMIT when you initialized the disk.

-Ryan



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