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Raid 5 to Raid 1 without loosing information..

Posted on 2013-05-25
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Last Modified: 2016-11-23
we have a Dell PowerEdge R710 that has a PERC H700, it has to virtual drives, the first one is OK in Raid 1 with two physical disks, but the second one is configured (I don´t know why) as Raid 5 but it only has two disks 600gb each, I know you need three disk so Raid 5 can work, so it is saying that we have a Degrated virtual drive...

If you into the configuration of the Raid, it says that we have one missing drive, we need to purchase another physical drive to be able to have the virtual disk in Raid 5.

The virtual disk is supposed to be 1,200GB, but we only have 600GB because it hasent been able to run in Raid 5, so, my question is the following:

Is it running on Raid 1 now until we insert another 600Gb disk?
Can I change it to Raid 1 instead of Raid 5 withouth loosing anything?

Best regards,
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Question by:marpanet
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rindi earned 500 total points
ID: 39196755
You are right in that RAID 5 needs at least 3 disks. But it is RAID 5 and so one of those 3 or more disks can die, and the array will keep on running (until another disk dies). In your case probably one of the disks has died and someone removed the bad disk and hasn't yet replaced it with a good one. The capacity though will stay the same, whether the array is complete or one of the disks is missing. You should just get the new drive and install it as soon as possible, and you should also get a spare drive so you can use it as replacement should another drive die.

If you would change the remaining 2 disks to RAID 1 you would loose half the capacity, Also, I don't think you can change from a higher RAID level to a lower one on the fly. The other way round can often be done, but it depends on the RAID controller.

Also, since RAID is no backup replacement, make sure your backups are fine.
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by:dlethe
ID: 39196857
No. because your RAID5 usable capacity is 2 x disk size, RAID1 capacity is  1 x disk size.
Now, you could do a backup & restore onto a RAID0, but I don't advise that due to risk of data loss.
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by:CompProbSolv
ID: 39196999
" but we only have 600GB": How have you determined this?

As others suggest, it sounded as if you had RAID 5 and one disk failed.  But... .if this were the case, you'd still see 1,200G capacity.
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by:marpanet
ID: 39199519
I think that the RAID 5 was working fine, but, they replaced that disk with one of 300GB, instead of 600GB, so the RAID marked as a drive missing because it can´t use the one with 300GB(I think). That´s the only explanation I can think of.... I know if you try to set up a RAID 5 with two disks it won´t let you from the start...

We are buying a 600GB so we can complete the RAID 5 again, Will it have a one disk failure tolerance?

Best regards,
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by:rindi
rindi earned 500 total points
ID: 39199586
Yes. With RAID 5 1 disk can fail and the array will still function, but degraded as in your case. You just have to make double sure that your backups are fine, and I would get the vendor of the disk to get it to you express so you can install it asap. If another disk fails then your RAID has failed... So you should act quickly. Also as I mentioned above, get an additional disk as spare. If there are still empty drive bays in your system you can install that spare drive in one of them and use the controller's utility to set it as a hot-spare. If one of the disks in your array fails, that hot spare then takes over and gets re-synced. That gives you a shorter time in which the array is in danger.
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by:dlethe
ID: 39200107
Marpanet - your data is already at risk, and you could have already encountered data loss.  RAID5 does not always protect against data loss when you lose a disk drive.  One unreadable block on any of the surviving disks is all it takes.

If data loss is unacceptable, consider going to RAID6, which means that there are dual parity blocks, so you have twice the protection. Your controller supports that RAID level also.
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by:marpanet
marpanet earned 0 total points
ID: 39226213
Thank you all for the information... We have bought one more drive, and contacted Dell, our information was indeed walking on a thin layer...
Dell support made a diagnostic on the remaining two drives and it seems that the last two drives of this virtual disc are failing…. So they are telling me that even though I insert the disk missing, the array fill be damaged and the information will be lost, I don´t know what type of damage the raid has, but we managed to backup all the information correctly, the only file that was corrupted was a 250GB one year old exchange database that was not in use and that we do not need it, so Dell will come with two new hard drive plus the extra one that we buy to set again the RAID and restore the information.
Before, this server was used for exchange and sql, but now we have another new server that holds the exchange, so I don´t know if it´s better to set RAID 1 with a hot spare than a three disc RAID 5, we don´t have space for an extra drive to make a four disc RAID 5. This I will check it out with the IT team, if RAID 1 is enough just for the SQL.
Thank you all!
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by:rindi
ID: 39226579
RAID 1 in my point of view is always better than RAID 5. It is easier to setup and maintain, and failures are usually easier to repair.
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Author Closing Comment

by:marpanet
ID: 39479058
Thank you for the information and tips.. Now everything is working fine.. Backups is the key..
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