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dell md3000 storage array

Posted on 2014-12-16
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Last Modified: 2016-11-23
I have a Dell MD3000 (15TB raw)  in a RAID6, single datastore, and have added an MD1000 (8 TB raw).  Using the Dell MDSM tool, I am adding the new 1TB disks in the expansion module to the RAID - one at a time.  Not actually sure how long this took for the first disk.  May have been a week.  The operation to add the second drive has been in progress for 3 days.
Is anyone aware of settings I should tweak during this process, like disable media scan.  Should I do this while my VM hosts are in maintenance mode?  Is it likely to be impacted by path redundancy issues or a firmware mismatch?  After adding the MD1000, I have an "Expansion Enclosure - Loss of Path Redundancy" error that I have been unable to resolve.
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Question by:HerrBall
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by:Philip Elder
ID: 40504107
Check your connections and/or cables between the two enclosures.

The error is indicating that either a controller or cable may be bad. I suggest changing the cables as a place to start.
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kevinhsieh earned 250 total points
ID: 40504159
You are trying to make this all a single RAID6 set? that seems like a really bad idea. 15 drives is a lot of drives in a single RAID group, and will take a very long time to rebuild. I would create a second RAID10 or RAID6 set from the second group of drives.
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Author Comment

by:HerrBall
ID: 40504718
Philip, I have checked and swapped cables.  The error stays with Enclosure 1, Channel 1 in this case.  Also reseated controller modules on either end.  The error cleared briefly (less than 5 minutes).  If I recall correctly, I did not swap controllers between the 0 (working channel) and 1.  Once I got the blue happy light, I started bringing the VM environment back up and opted not to do further troubleshooting at that time.
Parts and cables are requested from the 3rd party warranty provider, but they are dragging their feet.  Thanks for posting.  Oh, forgot to mention that I discovered if I flex the cable slightly at the controller connection, I loose the green link light.  It can be manipulated to go back green, but certainly more evidence to suspect cable/connection issues.
Any thoughts on the length of time it's taking me to add disks to the RAID?
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Author Comment

by:HerrBall
ID: 40504768
Kevin, in this environment, simple is good.  However, right now I think I agree and would like to backtrack.  Is there a way to do that?  I have added 1 disk to the RAID, with another in the process (still).  Neither has been added to my VM datastore.
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by:kevinhsieh
ID: 40505011
I have no idea if you can remove drives from a RAID group and shrink it. That might be a wipe and rebuild. :(. I suggest contacting Dell support.
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by:Philip Elder
ID: 40505257
I suggest starting with the bad cable or controller receptacle. With a flaky connection there will be a risk of poor performance but also data loss.

BTW, our MD3220 Dual SAS setups have a single RAID 6 setup (across 18-24 spindles) and we've not had any issues. Though where we have less drives installed the client was warned that adding drives would take a long time, put the array at risk, and impact performance. So far, only one did that and they are a non-profit that needed to stick within their budget.
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Author Comment

by:HerrBall
ID: 40505522
Hmmm, interesting.  So what you're saying, Philip, is that you don't see the down side to configuring two enclosures as a single RAID6 until the client wants to add disks?

Kevin, I don't see a way to remove a disk, except as you note, without wipe and rebuild.

BTW, the reseller who sold me the MD3000 and MD1000 has admitted that he omitted the SATA/SAS interposers on the drive sleds.  I'm running SATA drives.  I should have those parts overnight and see how that impacts my issues.  Will award points after I get a chance to troubleshoot in that environment again.
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Assisted Solution

by:Philip Elder
Philip Elder earned 250 total points
ID: 40505642
SAS disks have dual ports. SATA disks only have a single port.

Interposers mediate both path access and SAS commands to the SATA disks. That's disappointing.

We configure the RAID 6 array within the MD3220 SAS. We do not have any locations with an additional JBOD enclosure configured to the head shelf unit.

We've moved away from this setup to Scale-Out File Server cluster and Storage Spaces for our shared storage. It's a lot more versatile and cost wise is comparable.
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Author Closing Comment

by:HerrBall
ID: 40531631
This got abandoned while ill during the holidays.  Also had to wait on maint window availability, etc.  I appreciated the discussion, but none of it solved my problem.  The SAS/SATA interposers fixed the problem.  In retrospect, the error information from the Dell MDSM was much more specific that I realized.  It was also dynamic as I went through the troubleshooting and interposer installation.
I'm splitting points here.  The best advice I got out of this was to create a second RAID.  Before the interposer additions were complete, adding a disk to the RAID6 took 7 days.  Rebuilding a disk took 1 day.  I rather expect those times to go down with the interposers added to the 2 most recently added drives, but doubt I will take the hit to test.
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