snapshot with A5856A Raid 4Si card

[John Waller]

We have an rp2400 running a small database application with a RAID 4Si PCI SCSI controller and DS2110 disk system connected. Via irmd we have configured a raid 1/0 LUN setting the write policy to WRBACK (write-back) to gain performance.

To avoid having to close the database down two or three times a day we perform a snapshot of the database so we can copy it away to a safe location.

The issue we have is that when the system is being used the cp command hangs halfway through a file and never completes. Could this be an issue with the raid card cache'ing a block of data which should have been written to the snapshot volume.

We use the command "mount -f vxfs snapof=/dev/vg01/lvdata /dev/vg01/lvsnap /u/snapcopy" to make the snap mount and copy from /u/snapcopy.

[Thierry Poels_1]

hi,

did you reserve enough space for the snapshot LVOL? (I don't know exactly what happens when you hit the roof, but anyway...)

How about using RMAN for your online backups: easier(well uh;), safier & possibly faster.

regards,
Thierry.

[John Waller]

We have gone for a worst case scenario and have /dev/vg01/lvsnap same size as lvdata. As for RMAN I have not come across this product but as this works fine on all other systems without this Raid card I don't see why we need to add this extra bit to the process.

[Bernhard Mueller]

John,

do you have PHSS_27097 (11.0) or PHSS_27098 11.11) installed?

did you consider switching WRBACK off?

just my 0.02$

Regards,
Bernhard

[John Waller]

Bernhard, Thanks for the info about the patches, as it turns out we don't have these installed so thats my first job.

As for changing the WRBACK to WRTHRU thats the reason for this posting, the documentation states that WRBACK does give significant performance gain which is a big advantage for the application we use, but if WRBACK is definetly causing the problem then we will have to take the performance hit and change the policy.

[Bernhard Mueller]

John,

*if* only WRTHRU does the trick *and* performance is bad you might consider adding a second DS2110 (or do you already have two of them using all four SCSI channels of the card?)

Regards,
Bernhard
(I should be in sales, shouldn't I ;-)