Raid 5 performance

[Lee J milam]

It was mentioned to me by a fellow tech that when using Raid 5, you should use a minimum of 4 drives. Using only 3 causes poor performance, and going to 4 makes a large difference. Can anyone support this?

[Ruslan]

Hi Lee!

Note, that RAID5 level have the poorest write perfomance in comparsion RAID 1,10,0.
Increasing the number of disks in RAID5 array we can improve read perfomance.

[Ivan Ferreira]

As more drives in the array, the better the performance, but you still can use 3 disks in the array. If you will use 3 disks, ensure that the disks are the fastest, like 15k rpm scsi.

Also, as said above, you will improve read performance, write performance is reduced by the parity calculation.

[Fabian_Nowee]

What also wil help is a lot of cache esspecialy for the writes.

Writes wil be writen driectly to cache and will be destaged later, like a XP storage system.

Other systems like the EVA's works differtly. They need a lot of disks to create performance.

[Lee J milam]

These are all good points, but I know about these. My core question is weather there is a big improvement with 4 or more drives over 3 drives in a raid 5.

[Ivan Ferreira]

I think that you won't see an amazing change, but the performance should increase. The theory implies that, but only with real tests you will measure the performance increase.

[John Kufrovich]

Lee it will depend on the intended use. Is your application write heavy. How frequently will you be accessing your data.
Perhaps if you describe your intentions for the LUN we can tell you if it will help.

Read performance from all RAID levels is about the same, with exception of RAID 1 or RAID 1+0. Here you will see a slight increase due to load balancing.