Recommended config of MSA 20

[Kaj Laursen]

Hi

I have a MSA 20 with 12 500G disks, attached to a MSA 1510i. I'm running one large Raid 5 with hot-spare (so 11 disks and 5TB in tthe RAID). I have user-data (file share for students) on this.

Yesterday I had a disk fail in the MSA 20. It took 15 hours to rebuild the 2TB volume on the Raid (I only use 2TB right now). That got me thinking, that maybe the protection level is not enough.

I'm not going to run RAID 6 (ADG) - too slow.

What would you recommend - split in more Raid 5's, go for Raid 10 or something else? I'm willing to accept less than the 5TB.

How do the performance of the MSA 20 (in generel, and in rebuilds) compare to other SATA solutions?

Regards,

Kaj

[Dean Simiana]

Hi,
I have been considering the carve up of these devices for a while. We have previously had multiple MSA20's attached to the MSA1500 controllers and used to split our arrays over multiple shelves. This proved to be a disaster as shelves had a habbit of dropping off the SCSI Bus under extreme IO loads, rendering the arrays off-line!
Performance has not been such an issue in other configurations for me, so ADG was acceptable to minise this risk.
I have now decided that the lowest risk option with the fastes rebuild time is to run the entire MSA20 in a RAID1 configuration. Tests have shown that one array will be split over an even number of disks, allowing better redundancy per disk.
Rebuild time on the 250GB SATA disks is still a few hours on low priority, but it is just a disk copy, so there is no parity caclulations slowing it up.
Rebuild priority had to be set to Low for RAD5/RAD5+ADG as the controllers could not withstand the IO load and a parity rebuild.
I also have a Storage Tek Blade system, and it takes about 8 hours to rebuild a 2TB blade from parity and about 6 from mirror under normal IO.

Hope this helps.
Dean.