Dell MD3000i SAN Hard Drive Options

jwiang4u
jwiang4u used Ask the Experts™
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I am using a Dell MD3000i SAN in a 3 host iSCSI VMware implementation.  The current setup of the SAN is 14 146GB 15000 RPM SAS drives in a RAID 5 configuration with one of the 14 being a hot-spare.  I am running out of room in the configuration and I would like some advice on upgrade options.  Should I replace the current configuration with 14 2TB Near-line SAS drives setup as a RAID 10 or 14 600GB SAS drives setup in RAID 5?  Any alternate suggestions are welcomed also.  We run about 10 VMs in the environment with a mix of SQL, Exchange, and File serving.  There are about 50 concurrent users at this time in the environment.  I know that Near-line SAS is basically a SATA drive with SAS connections so there would be longer access times but i thought perhaps that RAID 10s boost in read and write times would help offset this.
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Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
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Commented:
What ever storage options and disk sizes you select, I would recommend RAID 10, with 2TB disks.
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
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Commented:
Sorry, ignore that. RAID 10 with 600GB SAS. If that's enough storage.
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
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Commented:
Is 3.6TB enough storage worth with 12 x 600GB, and two spares.
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Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
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Commented:
So RAID 10 with 12 x 600GB, 2 spares, double's your current capacity, from RAID 5, approx 1.7TB. With the benefits of a much faster, better performing datastore, and double the capacity.

Are you noticing any performance issues with RAID 5 to change to RAID 10?
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
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Commented:
What's your growth over the next few years, any more VMs? Whats the growth of the Exchange store, and SQL?
jwiang4uIT Director

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Commented:
I am not noticing any issues right now but i thought that if I am going to have to bring the entire array down for the upgrade that it is probably worth evaluation the RAID level options also.  I have read that the write performance and rebuild times on RAID 5 can be problematic as data needs grow and I know that there is a big benefit to RAID 10 in both rebuild and write performance.
first consideration - use raid 6 instead of raid 5.  you will lose some space but going with larger drive sizes increase the time needed to recover from a failed drive.  
I would use 14 600GB 15K SAS drives.  
We are running (8) 300GB 15K SAS drives internally(raid6) on our VM and a MD3000 with 14 1TB NL SAS drives.  We see a difference in the performance between the two.   We have changed the layout of the drives several times in the MD3000 to get better speed and still just cannot compete with the faster spindle times.

Now - we had to run several tests to stress out the system.  Our normal VM's did not push the limits.  We have a few exch2010 boxes, SQL 2008 and about 18 other servers - ad's and such running.

Big extra note.  VMWare will not see a drive bigger then 2tb.  when you make the raids keep this in mind.  we run smaller drives (1.8 or so) and use all spindles to max out speed.

jwiang4uIT Director

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Commented:
Have you noticed any write performance degradation with RAID 6?  I had thought about going with RAID 6 but had read online that the increased complexity of second parity stripe afforded by RAID 6 can really hurt your write and rebuild speeds. http://www.techrepublic.com/blog/datacenter/raid-6-do-you-really-want-it/119
jwiang4uIT Director

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Commented:
@hanccocka

We are currently using about 1.1 TB out of the 1.7 but i expect that we will hit the 1.7 mark by Q1 on next year.  I think that 3.7TB should last us for quite awhile.  Do you know anything about the MD1000 expansion cabinets?  I think that this would be a fail-safe for me in the future if i need to add more storage beyond 14 600GB SAS drives.
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
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Expert of the Year 2017

Commented:
I think it would depend on is 3.6TB going to satisfy your growth over the next few years, compared with RAID 5.
Top Expert 2014
Commented:
Got room in the rack for an MD1000 expansion chassis? That would let you keep the old disks and create another array with some new ones. You could for example put some nearline SAS disks in it for Exchange database, assuming 2007 or 2010 the IOPS are low enough for 7.2K disks.
jwiang4uIT Director

Author

Commented:
@andyalder

I do have room but I wasn't sure if there was any performance degradation when using an MD1000 expansion chassis vs disk contained with  the same chassis.  Any thoughts?
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
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Expert of the Year 2017

Commented:
on of the features of the MD3000, is the ability to add up to two MD1000s.

You shouldn't experience any performance issues by adding another one (or two), if you have the budget.
Top Expert 2014

Commented:
Overall performance would increase - you'd have more disks in it. Performance on the current LUN should be degraded by a tiny bit because the cache would be shared by both sets of disks but it's not likely to be noticed.


@jwiang4u  
For the raid6vsraid5 performance on writes because of added stripe.
 We have not seen a major hit.  I think a lot depends on the card used. As long as the card can think faster then the drives can dump the buffers your ok.  I know there will be a hit to the sys-performance if a rebuild takes place - but you have that on 5 as well.  Most of our raid6 deployments are 8 or more disks

for the MD1000 - it would be slower than say - adding another dm3000 with independent interfaces/links to the server but far less expensive.  We have already started looking at the 1000 addon 'just in case'  It is amazing how these people are buring through drive space.

dan
jwiang4uIT Director

Author

Commented:
Right now i am thinking that i will add an MD1000 cabinet with 7 600GB SAS drives in Raid 5.  That will give me room for expansion and less hassle then bringing the existing array down for reconfiguration.

Has anyone used any of the traditional SAN alternatives like Scale Computing or the new Drobo B1200i?  I think Scale Computing scalable architecture to be really interesting and they have pretty good throughput according to there specs anyway.
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
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Expert of the Year 2017
Commented:
We are currently test new Drobos, with SSDs.

But I think the addition of a MD1000 is best solution.

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