topic Raid 0+1 or Raid5 in Disk Enclosures

Raid 0+1 or Raid5

Ayman Altounji — Fri, 30 Nov 2001 00:00:00 GMT

Hi,

I have got a new Proliant ML370 with a Smart-5304 that I purchased. This server is to be used as a Btrieve Database server. Now I am wondering what would be my best bet as for Raid configuration. I have two 18.2 that I want to install Raid1 (in the expension bays) and I purchased 6 X 38.4gigs 10000rpm drives. What would give me the best performance (considering it's a database server). Should I install it 6 X 38.4(raid5) or Raid 0+1 (3 X 36.4 + the other 3 mirrored)?

Re: Raid 0+1 or Raid5

Ayman Altounji — Thu, 27 Dec 2001 00:00:00 GMT

Is this and OLTP or DSS database? And what are your page sizes? Anyway not to answer with a question with questions...., as a rule for a database choose RAID 5. It will allow for better failover and the cost overhead is not as high as with a mirror. A stripe will give you better performance but not allow for a failed drive. In a mirror you will lose half of the drives storage. When doing your RAID set ensure your chunk size matches the chunk size for your database, (8k, 16, 32k, 64k, etc * - smaller is generally better for OLTP systems) this will allow for a best performance and you will only drop about 18-20 percent of overall storage to your failover. Also check your write thru vs write back configuration, in a OLTP configuration read ahead gains you little to nothing while with a DSS it will mean a great deal. A combo of both might be better if you can lay your index files, logs and tmp spaces on a mirror and the data on a RAID set. Good luck.

Re: Raid 0+1 or Raid5

Ayman Altounji — Tue, 15 Jan 2002 00:00:00 GMT

performance issues in a database are simple to cure. add more drives. more spindles (disks) will give you more performance. you need 4 times the performance you have right now you must have 4 times the disks you have right now.
in your case 4 disks raid 5 (for DB) will give you some better read performance than raid 0+1 (measured on the same system with iometer benchmark). but the write performance will be at least twice as good with raid 0+1.

when the compaq proliant 8500 (8 cpus / 4 gb ram / nt / sql) won a new world record with 44.000 transactions/minute two years ago there were 380 (!!!!) disks attached to the system (multiple smart 4200). when the number of the disks was reced to 200 the tpm benchmark showed only 25.000 TPMC/min.
do you get the message ?

ernesto from germany