MSA500G2 array configuration

[yzenezy]

Hi,

We're running CentOS 4.4 on a DL360G5 connected to an MSA500G2 via a 642 controller. The DL360G5 has two mirrored SAS drives for the OS and the MSA500G2 will serve as a data store (as a file server). We're also contemplating connecting an older DL380G4 via the second SCSI port later on using the array in SSP mode.

The array only has 6 x 146.8GB, 10krpm drives currently and I'd like to know the best configuration for the array. At some point we will need more storage so I anticipate expanding the array then by adding more drives of the same capacity/speed.

Is it better to configure it in RAID5 5+1 and present one large logical drive to the OS or create many smaller logical drives to present to the OS? I expect to use linux LVM to configure the presented volumes in any case so I'm interested to hear your opinions on linux LVM striping as well. What's going to be the best configuration for flexibility and performance?

Thanks in advance,

Tom

[Jefferson Humber]

Tom,

IMHO, RAID 1+0 and then carve it up in the O/S into smaller LUN's.

Jeff

[yzenezy]

Hi Jeff,

I appreciate that RAID 1+0 will give the best performance. It would be nice but we can't afford to lose half the storage to redundancy right now. I was thinking that RAID5 5+1 (or even disposing with the spare to just RAID5) would still give a good performance with redundancy.

You suggested multiple LUNS; any ideas on how big each logical drive should be? Will striping the LUNS through OS LVM give a performance boost on linux or am I wasting my time?

I've been reading a few other posts on the forum. Is it valid to apply the techniques discussed for other array systems such as the XP12000? I'm assuming that 'the more spindles you have, the better performance will be for RAID5 configurations' is a generic rule that can be applied to all disk array systems. Can I make a RAID5 too big (i.e. the disk enclosure of the MSA500G2 has 14 bays)? Any comments?

Thanks again,

Tom

[Jefferson Humber]

Tom,

I can understand your concerns with RAID 1+0, it is expensive to implement since you loose 50% of the available disk space to redundancy.

RAID5 is OK, as long as you can live with the performance penalty. Whether or not you implement the online spare drive is really down to how much you value the data and how much downtime would cost you to run a restore operation. Obviously RAID5 can sustain one HDD failure, is the probability of a 2nd failure before you can replace the failed drive acceptable to your business ?

As for the LUN count presented to your O/S, it depends how many LUN's you need really for your application. If you only need one, the just present one. I personally wouldn't bother with host based striping software. It adds processing time to the system, and is one more thing to go wrong in my opinion. Sometimes keeping it simple is the best approach.

You can always add more HDD's to your array at a later date anyway, so performance/resilience could improve over time if you can afford too.

Hope this helps,

Jeff