number of drive in Raid5

[gsavy]

Hello

In EMC documentation we can read that Raid 5 is made with 3 to 16 disks and best performance are reached with 5 or 9 disks.

But what about the performances if I create a Raid 5 StorageGroup composed with 7 disks, how much worse than 5 or 9, 10% 30 % ???

And between 6 , 7 , 8 , 11 disks what is worse / best

Do you have this kind of information ?

Thanks for your help

 

[mrdenny]

You'll be hard pressed to find any documentation about how much better or worse it will perform as easy array and RAID group will perform differently based on it's load. The best way to see will be to create a RAID Group on your unit and test it under your normal load and see how it reacts.

Denny
MCSA (2003) / MCDBA (SQL 2000)
MCTS (SQL 2005 / Microsoft Windows SharePoint Services 3.0: Configuration / Microsoft Office SharePoint Server 2007: Configuration)
MCITP Database Administrator (SQL 2005) / Database Developer (SQL 2005)

My Blog

 

[Korwin]

That recommendation didn't make sense to me either. I assume you are referring to Clariion best practices. I could agree with 5 through 9, but I don't understand the 5 'or' 9. I think its a cosmetic thing as the DAE's hold 15 disks.... so 5 or 9 would allow you to have a nice pretty 3 raid groups of 5 disks each in 1 enclosure, and/or a 9 disk raid group and a 5 disk raid group with 1 left over for a hot spare.

Its 'best' to have about 4 or 5 luns per raid group. If you make your disk groups too big, you may get yourself into a situation where you have 10+ luns on a single raid group. This would be an issue if several of those luns had heavy IO at the same time. Also large raid groups take longer to rebuild a failed drive.

 

[mrdenny]

Keep in mind that 10+ LUNs in a RAID group is ok, if they are all low IO LUNs. It's all about making sure that you are keeping your RAID groups below the limits of the group.

Denny
MCSA (2003) / MCDBA (SQL 2000)
MCTS (SQL 2005 / Microsoft Windows SharePoint Services 3.0: Configuration / Microsoft Office SharePoint Server 2007: Configuration)
MCITP Database Administrator (SQL 2005) / Database Developer (SQL 2005)

My Blog

 

[gsavy]

ok thanks for sharing your vision