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622

answers:

1

So we've decided on an EMC NX4 for our storage setup.

Database workload
Write: ~220 IOPS
Read: ~6 IOPS

Web workload
Write: ~10 IOPS
Read: ~55 IOPS

I had planned to go for 5 x 15k SAS disks in RAID 10 + hot spare for our databases, and then a 7 x 7,2k SATA RAID 6 + hot spare for our web data. However, EMC conveniently forgot to mention that the first 5 disks had to be setup in a RAID 5 for the system volumes. We haven't signed the agreement yet, but I obviously need to come up with a new disk layout for this to work out.

They suggest we put the 15k SAS disks in a RAID 5 + hot spare, but won't this rather quickly give me write performance issues? Besides the RAID 5, we'd then be left with a 6 disk RAID 6 leaving us 4/3TB usable data depending on hot spare/not.

Alternatively we should stick with the RAID 10 for our DB's and put our 1TB 7,2k SATA disks in RAID5 - Though I'm not fond of the rebuild time and insecurity of running these in RAID5. The raid level suits web data much better however.

So we basically have three choices as I see it:

6 x 15k SAS RAID5 for System Volumes + DB data+log + hot spare
6 x 7,2k SATA RAID6 for file data + hot spare

OR

6 x 7,2k SATA RAID5 for System Volumes + file data + hot spare
5 x 15k SAS RAID10 for DB data+log + hot spare

OR

5 x 15k SAS RAID5 for System Volumes + DB Data
2 x 15k SAS RAID1 for DB Log
1 x 15k SAS hot spare
4 x 7,2k SATA RAID5 for file data + hot spare

Option 1 may have write performance issues. Option 2 can become dangerous during rebuilds. Option 3 is good for DB performance but leaves us only 2TB usable file storage, meaning we'll soon have to expand with an extra shelf - and at that point convert our file data to a RAID6.

+1  A: 

Personally, I would go with option #2

6 x 7,2k SATA RAID5 for System Volumes + file data + hot spare
5 x 15k SAS RAID10 for DB data+log + hot spare

Regards K

Khb
That is without doubt the one that is most optimal in regards to us having good DB performance as well as plenty of file storage. I just don't like the fact of storing 5TB of data on a RAID5 array, using SATA drives. It may however be the best solution for us, until I can warrant adding a 2nd shelf.
Mark S. Rasmussen
I personally would have chosen SAS for the system disks + file data, 2x15kSAS disks in RAID1 with a 146GB capacity, but I don't know if that is enough for you. 5TB on SATA would be a slow rebuild.Possibly two pairs of RAID1, and use 1 disk as global hot spare
Khb
The system disks MUST run RAID5 as per NX4 requirements/design. And 146GB SAS disks for file data will not cut it, we need TBs of storage, not GBs. 5TB on SATA is a slow rebuild, that's also why I want to upgrade to RAID6 asap. It seems RAID5 will have to do until we can get another shelf.
Mark S. Rasmussen
Hi again. When you say that the system disks for the NX4 have to be RAID5, are you sure that you can use them for your files as well?
Khb