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Hardware RAID with ZFS on Nexenta (OpenSolaris)

Posted on 2013-01-06
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Last Modified: 2013-01-11
I am using Nexenta (Open Solaris) for its ZFS features on an Appliance that I use.  I was planning to set the disks as JBOD, but when I got down to it, the LSI MegaRaid SAS 8708EM2 controller did not support JBOD.  So, I had to set each of the 24 1Tb SATA disks as its own single disk RAID0 configuration.  This, at least, allowed the disks to be seen by the installation.  I mirrored the boot disks and used zpool not the Nexenta menu to create a 3 x 6disk raidz3 configuration with 3 hotspares.  The zpool will be used as an Iscsi target for remote VMware datastore.  Is this an efficient configuration or how could this have been done better with Nexenta.? Thank you for your help!
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Question by:theoradically
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by:andyalder
andyalder earned 100 total points
ID: 38748749
It's not that efficient since you could have bought a cheaper JBOD HBA rather than a RAID controller; you'l probably still get the benefit of the write cache on the controller and have the restriction that it needs enterprise drives although it may have the sense not to fail flakey drives that go into deep recovery as it's in a RAID0 environment.
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by:dlethe
ID: 38748770
ZFS is designed for JBOD controllers.  Without a JBOD controller then you will suffer big performance hits due to the mandatory flush-on-write.  RAID0 disks behind a MegaRAID controllers do not behave the same as true JBOD target devices.  There is still caching and some degree of virtualization.

I am sure you will have no problem having volunteers lined up if you want to swap a MegaRAID for a 92xx JBOD equivalent LSI.  IN fact, you may even get TWO LSI JBOD controllers for this MegaRAID.
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by:theoradically
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I am stuck with the hardware and looking need the free "open solaris" in a commercial environment.  How should I set this up for best performance?  If I use the hardware RAID10, how should I set up the zfs configuration?
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dlethe earned 400 total points
ID: 38749205
If you want best performance, then use the raid controller to create separate RAID1 devices.  Then do a stripe on zfs

so if first 3 striped devices appear as c0d0,c0d1,c0d2

zpool create mypool c0d0 c0d1 c0d2

This gives you reasonable config. and you end up in this example with a 6-drive RAID10, even though ZFS thinks you have a 3-drive RAID0.

ZFS will still give you all the benefits, but the additional flushing overhead to insure data integrity will be minimized due to the controller write cache.
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