Poor Disk Performance on T610 + software RAID

[akrherz]

Hi all,

After reading the subject, you'll are probably like 'duh', but anyway, was curious if anybody had suggestions for me. I have a Dell T610 with a bunch of 1.5 TB drives inside it. I put 6 of these together in a RAID5 (software) on a RHEL5 VM. The performance hasn't been terrible, but it isn't good, that is for sure (lots of lagging, slow write rates, etc..). Anyway, I suspect what I did is bad bad bad, but was curious if anybody else had figured out a way to make this work well. I don't have a hardware RAID option and my requirement is to have a lot of space available for one VM to use and NFS serve out.

Thank you,

daryl

[DSTAVERT]

Without a hardware RAID controller and writeback caching enabled (Need a Battery Module to support this) performance will be poor.

RAID 10 may give you better performance with what you have.

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[idle-jam]

Fully agree with DSTAVERT, you really need a hardware raid controller with as much cache memory (battery backed) as possible. The differences is alot for my pass experience ..

iDLE-jAM | VCP 2, VCP 3 & VCP 4

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[akrherz]

Thank you both. Yes, but without ESXi, I have plenty of software RAID5s that perform well enough for my needs. I was curious if there was a trick when dealing with the combination of software raid and ESXi.

daryl

[DSTAVERT]

ESXi does not support software RAID. It also doesn't support individual RAID LUNs over 2TB so your RAID controller would need to allow you to create virtual LUNs from your large array. Find a hardware RAID controller. Ebay or similar if you need to.

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[DSTAVERT]

The best you can achieve will be individual disks. You can replicate VMs from disk to disk.

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[akrherz]

For what it is worth, I upgraded the guest OS to RHEL6 and I am getting disk IO rates I would expect.

[idle-jam]

Great to hear about this. Can you share with us what sort of improvement are you getting? from X seconds to Y seconds.

[akrherz]

Previously, I was getting about 10 MB/s writes.  Now I am upwards of 120 MB/s.  That's good enough for me

daryl

[DSTAVERT]

I would really do some testing before you do anything serious. I would be concerned about a hard crash. Make absolutely sure you don't have write caching enabled.