RAID5(4+1) vs RAID5(8+1)

in a 41 raid group you'll get 125% of the IOps per GB of a single drive in the RG where in a 81 you'll get 112.5%.

In performance calculation you'll always count ALL drives, which is fair snice the write penalty dealt with the overhead.

Traditionally I'd have gone for creating a META LUN over 2 RGs which both are 41 rather than 1 LUN in a RG which is 81. Twice a 41 has the performance of 10 drives, where a single 81 has only the performance of 9 drives.

We are thinking about RAID5(8+1) because it will save us a lot of disk when compared to RAID5(4+1).

Not sure if it is the right move but want to know if there is a way in Unisphere to create a RAID5(8+1)? I think it defaults to (4+1).

Thanks.

I haven't worked with Unisphere yet, but I assume that when you select RAID5 it defaults to 5 disks, but if you set it to manual, you can add as many disks as you like, right ?

Yes, when you are creating RAID Groups, you can choose how many disks you want to put in that RAID Group. You can also manually choose the specific disks which you want to be a part of this RAID Group.

A RAID5 Group of 10 Disks will create a 9+1.

A RAID5 Thin Pool of 10 Disks will create two 4+1’s.

Oh yes that was just me being dumb. We can choose as many disks as you want and the system will RAID it depending on that.

So my understanding is that when you create a RAID group with 9 disks, we are create a LUN with size 500GB, are we spanning the parity accross all the disks? Is that same as creating RAID5(8+1)?

If we created a pool with 10 disks how does it lay out in the backend? Is it going to be RAID5(4+1) or (8+1)?

Appreciate it.

So my understanding is that when you create a RAID group with 9 disks, we are create a LUN with size 500GB, are we spanning the parity accross all the disks? Is that same as creating RAID5(8+1)?

Just to address this specific point, when you create a RAID Group with 9 drives it does not yet have any RAID type associated with it. When you create that 500GB LUN you define what RAID type you want it to be. You could make it RAID 5 which would distribute the parity in an 8+1 configuration. You could also choose RAID 6 which would distribute the parity in a 7+2 configuration. There are other options as well. The point is, nothing is set for the configuration until you bind your first LUN on the RG.

We have 3 SATA II SSD disks. There are different size than our fiber channel disks.

I am thinking it will not be a good idea to mix disks of different sizes in the same pool. Am I correct or is there a reason to use SSD disks in combination of fiber channel disks even if they are different in size.

Thanks a lot to everyone for helping me in here. I have a better understanding now.

You can mix SSD, FC and SATA in a single Pool if you have flare release 30 on the array. See the following white paper for more information.

EMC FAST for CLARiiON—A Detailed Review

UPDATED LINKS

http://powerlink.emc.com/km/live1/en_US/Offering_Technical/White_Paper/h8234-fast-clariion-wp.pdf

POOLS

White Paper: EMC CLARiiON, Celerra Unified, and VNX FAST Cache — A Detailed Review

http://powerlink.emc.com/km/live1/en_US/Offering_Technical/White_Paper/h8046-clariion-celerra-unified-fast-cache-wp.pdf

glen

Hi kelleg,

Are you able to provide another link to the "EMC CLARiiON Virtual Provisioning—Applied Technology" document, as that one is not working?

updated the links - thanks for pointing this out

Awesome, thank you.