be1977
Contributor
Contributor

RAID 10 Drives 300GB vs 146GB for ESX Data Store

Jump to solution

I have 5 drive bays available in my Clariion SAN enclosure. Given the option of 300GB 15K drives or 146GB 15K configured for RAID10 drives which would be preferred?

Obviously I could provision a lot more VM's with the larger 300GB drives, but would I hurt performance too much with the limited spindle count?

0 Kudos
1 Solution

Accepted Solutions
RParker
Immortal
Immortal

> 300GB 15K drives or 146GB 15K configured for RAID10 drives which would be preferred?

BOTH are identical. The only difference being space.

It depends on how big you want the VM's. Just because you have 300G drives, doesn't mean you have to allocated the entire volume as a LUN, you could use it for something else, like extra storage. Eventually you will run into performance issues with only 5 spindles, but I will still go with the larger drives, because you never know what you may need.

Plus you can keep the storage for SAN snapshots also, or maybe archive of VMs, or ISO's.. you can do a lot with extra storage, but I wouldn't base the decision solely on performance, storage is still storage, you can always use it later.

View solution in original post

0 Kudos
10 Replies
mcowger
Immortal
Immortal

5 spindles isn't a lot of performance, but only you can evaluate whether its acceptable performance.

Dont forget that a 300GB drive will likely have 2x the rebuild tim in case of failure, doubling your exposure to data loss.

--Matt

--Matt VCDX #52 blog.cowger.us
0 Kudos
kjb007
Immortal
Immortal

As mcowger stated, 5 spindles is not a lot to worry about performance hits, in my oppinion. Since they're both running at 15K, I don't think you're going to take much, if any, performance hit with one or the other. I would, instead, judge what I have to load on the space instead. Are you going to be running high I/O OLTP databases? I would use the 300 GB and get the most out of my enclosure. Rebuild time is also an important consideration. You're also talking about RAID 10, so you're already reducing the amount of space quite a bit, and 5 drives in a RAID 10, is going to give you ~400 GB with 146 and ~700 with the 300's. Again, what kind of vm's are you running? I would instead run RAID 5 and get the most out of the SAN.

-KjB

vExpert/VCP/VCAP vmwise.com / @vmwise -KjB
0 Kudos
be1977
Contributor
Contributor

I will be running web based server software, Citrix, and possibly Exchange 2007. I don't have any plans to virtualize my Databases at this time.

I was leaning toward RAID 10 because some of the other threads I have read indicated that RAID 5 performed poorly as a Data store, but perhaps they were not using a SAN with write caching enabled?

0 Kudos
kjb007
Immortal
Immortal

You have to keep in mind that 'RAID5 performed poorly' is a relative statement. What is poor to someone, may suffice for you. Don't discount based on a statement without testing in your environment. The person that posted that may have a very high requirement for disk I/O, whereas you may not. I would test the config and see how it performs for you.

-KjB

vExpert/VCP/VCAP vmwise.com / @vmwise -KjB
0 Kudos
RParker
Immortal
Immortal

> 300GB 15K drives or 146GB 15K configured for RAID10 drives which would be preferred?

BOTH are identical. The only difference being space.

It depends on how big you want the VM's. Just because you have 300G drives, doesn't mean you have to allocated the entire volume as a LUN, you could use it for something else, like extra storage. Eventually you will run into performance issues with only 5 spindles, but I will still go with the larger drives, because you never know what you may need.

Plus you can keep the storage for SAN snapshots also, or maybe archive of VMs, or ISO's.. you can do a lot with extra storage, but I wouldn't base the decision solely on performance, storage is still storage, you can always use it later.

0 Kudos
RParker
Immortal
Immortal

You can't do a RAID 10 with only 5 drives. RAID 10 is RAID 0 across RAID 1's. So in this case you can have 2 RAID 1, then RAID 0 Across the two, but that's a HUGE waste of spac

You will only end up with 600G NET, then what are you going to do with the 5th drive.. RAID 5 nets 1.2TB

RAID 5 is the way to go, whoever told you that RAID 5 doesn't perform, ask them to product facts, not hype. WE use RAID 5 for everything, and haven't had any performance issues, even across 28 Disks...

be1977
Contributor
Contributor

Thanks for the replies. I know I can't use 5 drives to create a RAID 10 array. I have 5 drive bays available in my Clariion enclosure, my thought was to use 4 drives for the RAID 10 and the 5th for a hot spare.

As you asserted using all 5 drives to create a RAID 5 array would net me a lot more storage space. If RAID 5 performance is not an issue for Exchange (My most demanding VM application) that would be the preferred configuration.

This enclosure already has one 10K 300GB Hot spare, do you think that is still sufficient for the enclosure if I add five 15K drive in a RAID5?

0 Kudos
Nick_F
Enthusiast
Enthusiast

I'd recommend the RAID-5 option to. According to EMC the Clariion's are highly optimised for RAID-5 so there's not much of a performance benefit using RAID-10. We're using mostly 5 disk RAID-5 groups on our Clariion CX3-20 (15k 300GB drives), personally I'd have preferred to use 146GB disks and more spindles but so far we only really see I/O bottleneck issues during conversions.

On the hot-spare issue, we were recommended to have a hot-spare per 30 spindles. Not sure how many existing spindles you have in your SAN but regardless I'd change that existing hot spare to be a 15k drive otherwise you'll degrade the performance of any 15k RAID group if might get used in (assuming you configure them as global hot spares)

dmckenzie
Contributor
Contributor

You can't use the 10K RPM 300gb drive as a hot spare for the 15KRPM 300gb drive. The CLARiiON requires identical hot spare drives. The best practice for hot spares is one HS for every 2 DAEs (so 1 per 30 drives), but you also need at least 1 hot spare for each type of drive in the array. If you are going to be using RAID 10, you'd be able to fill in another 24 drives before you need to install a second 15k 300gb hot spare. As for the CX being highly optimized for RAID-5, this is true. Generally in a VMware environment at customers I have worked with, they run their datastores on raid 5. Any RAID 10 luns are generally RDM'd directly to the virtual machines that require it, such as the SQL servers.

Hope this helps.

-Dave

0 Kudos
beckhamk
Enthusiast
Enthusiast

let me state this, we had the same concern last november when we moved into the ESX world with a HDS AMS200 FC unit. We had no idea about how well R5 or R10 would perform. So we purchased 30disks and set up each array in R10 7d+7d. The performance was stellar, then we obviously needed more disks. So before we did that we had HDS review our performance logs and found out we where barely using the unit. I mean serioursly like no more than 10 ios per drive. So we ended up using storage motion to move the vmdks from one array to the other, then reconfigured using R5 and moved them back. We dont even notice the difference between the two raid configs. We originally did run iometer testing on many difrerent configs and raid levels. But we wanted the best performance vs disk, now that we know how well the unit runs with vmware with all of the servers (25 heavy web servers) the R5 options works perfectly. I would suggest using the R5, and if needed using R10 on a smaller subset in case you need to use both.

0 Kudos