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Author Topic: Migrate to RAID 5 2 disks + 2  (Read 2641 times)

Legion

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Migrate to RAID 5 2 disks + 2
« on: July 09, 2015, 11:34:47 PM »

Hi to a great forum you have all so far been very helpful and informative.

I have recently bought this item and have been enjoying setting the whole thing up. 
I originally put 2 disks into slots 3 and 4 in standard format knowing that I wanted to add two more disks before I deployed the server.  In Standard format I have already transferred data which I would prefer not to redo. All data is (now) on Volume_1 - disk 3.
So I have
Volume_1   : Standard  - disk 3
Volume_2   : Standard  - disk 4

I have now purchased two more identical disks and have installed them as Disk 1 and Disk 2, so far unformatted.

In the wizard I get to step 1 and it correctly identifies the new drives.
I request 'Reconfigure to RAID 5'
The next step shows the two existing disks

Volume_1  EXT 4  size  disk3
Volume_2  EXT 4  size  disk4

My problem, and it may not be a problem but I don't want to continue until I clarify the point, is that;
I can only choose either Volume_ 1 or Volume_2 but not both.  I want all 4 drives to be configured as a RAID 5, but it seems only choosing one that the other will be left as a standard drive which I don't want.

The instructions in the manual are not clear as they only show one drive installed before migration.

How do I ensure that the migration to RAID 5 does so with all 4 drives.

Thanks
« Last Edit: July 09, 2015, 11:37:47 PM by Legion »
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ivan

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Re: Migrate to RAID 5 2 disks + 2
« Reply #1 on: July 12, 2015, 10:48:41 AM »

For a start I would ask why do you want to use RAID 5?  Yes, it works quite well with SCSI disks used in a server with a hardware RAID controller.  When we changed our storage array from SCSI to SAS/SATA we dumped the idea of RAID 5 because of potential problems.

Part of the SATA specification allows for UREs (Unrecoverable Read Errors) and if one of those just happens to be where the PARITY information is written on the disk then you loose the array and there is something like a 40% chance of that happening.  It is better to use RAID 1 or RAID 1 + 0 (RAID 10) where you are not relying on PARITY information to keep track of where your data is.

No matter what setup you end up using, if you value your data make sure you have reliable, tested and proven backups.
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Legion

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Re: Migrate to RAID 5 2 disks + 2
« Reply #2 on: July 13, 2015, 12:16:05 AM »

So yeah, thanks for answering the question.

As it turns out I think in answer to my original question is, without going off onto some useless tangent, I can't.  I don't think the software on the unit allows it.  To remedy the problem I pulled the second drive and reformatted it as EXT4, whacked it back in and was able to set up the RAID 5 with all four drives.
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ivan

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Re: Migrate to RAID 5 2 disks + 2
« Reply #3 on: July 13, 2015, 06:41:23 AM »

Sorry it wasn't the answer you were looking for but the RAID 5 'reliability' has been on my mind for a few days (a client almost lost all his data because his NAS, not D-Link, refused to read anything off the disks because of a bad parity stripe.

If you are happy with what you have, good.  Just make sure you have good backups of your data.
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