Disk Mirroring and Striping

[Jerry Owens]

Am in the process of procurring 2 new L 1000 servers running HP 11.0 with a group of (10) SC10 disks shared between them. Would like to mirror them and then stripe a portion of them. Is this feasible?

[Stefan Farrelly]

It most certainly is feasible to stripe any disk(s) you want. If youre going to stripe and mirror then use the lvcreate -D (distributed) option.

[John Palmer · Accepted solution]

Yes,

Mirroring requires the add-on MirrorDiskUX software for HP-UX.

Striping is a normal feature of Logical Volume Manager (LVM).

Mirroring and striping of the same logical volume can only be done at a physical extent level. Search the ITRC for information on extent based striping.

Another alternative is that HP have recently made RAID controller cards available for the L series which can use the SC10 disk subsystem.

Hope this helps,
John

[Vince Inman]

Certainly is feasible and IMO recommended. You can use the -D (distributed) switch on the lvcreate command to do this very easily.
As well, you will need to set the -s g switch on the lvcreate command (pvg strict). Before starting, setup two PVG's for the VG in the /etc/lvmpvg, say VG_primary and VG_mirror and you'll be able to do it with one command:

lvcreate -l <# extents> -n -D y -s g -m 1 /dev/vgxx

[Tim Malnati]

There is a big difference between block level striping ( -i & -I options ) and extent level striping ( -D option ) in terms of efficiency and throughput. Block level is best, but the Mirrordisk product does not allow both block level striping and mirroring in the same volume. If you are going to do extent level striping (still a good idea), it is best to have extents as small as possible. The default LVM extent size is 4MB. Reducing it to the smallest value (1MB) is best but there are limitations in the overall size of the volume group table which may prevent you from reducing the PE size this far if you are using large disks or you have many physical disks allocated for the group. In any case, adjusting PE size can only be defined at the time of volume group creation, so you may need to rebuild the volume group first to achieve a smaller PE size. The new raid controller sounds like a good option where it will probably allow for block level striping with the controller handling the actual mirroring at the hardware level. I have not played with it, so I can't be sure. But I wonder how this controller would fit into a shared machine environment.