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In a Raid can I operate with failing hard drives

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Last Modified: 2017-05-17
I has a Dell PowerEdge T710 which was originally purchased for a exchange server but was never used. I want to use it now to mirror the main server (also a PowerEdge T710) is has 2 hard drives RAID 1 for the OS and then a set off drives for the data RAID 5
One drive of set one (OS) and one of the RAID 5 or dead. Since I will only use this server for backing up and theses hard drives are very expensive [SCSI (SAS) RMP 15k] is there a way I could I just ignore the dead drives? (to my knowledge the RAID 1 yes but the RAID 5 one missing will kill the others)

Server 2008
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Adam BrownSenior Systems Admin
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If you are just going to use the server for backing up then you can reconfigure the RAID.  If I understand correctly, you have one bad drive from each RAID1 and RAID5.  I would just trash the two bad drives so you should still have at least 3 drives left.  Enough for a RAID5 reconfiguration and reinstall Windows.  Will that work?
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I assumed that the asker is trying to reuse old hardware unless otherwise stated.  RAID5 offers the best protection with the currently available hardware (3 hard drives left).

I would also stay away from RAID0 and RAID1.  If the main purpose to re-utilize the server then at least RAID5 is recommended.  If the budget for new drives is available then it's a different story.  He can opt. for a better RAID configuration depending on the budget and hard drive slot available.
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@Wayne88:  Why would you avoid RAID1?
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PowerEdgeTechIT Consultant
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Unlike CompProbSolv, I would suggest staying away from raid 1 and always using raid 5.  The speed difference would not be noticeable in most cases and the protection is much better.
That is the first time I have ever heard someone (this decade) recommend RAID 5. I'd recommend RAID 1 ... or RAID 10 if volume size and/or performance matter.

Your RAID controller also makes a difference. If using the S300, then you should absolutely not be using RAID 5.

You could also use SATA drive instead of SAS ... they aren't as expensive. Just don't use cheaper desktop/laptop/NAS drives.
Andrew Hancock (VMware vExpert PRO / EE Fellow)VMware and Virtualization Consultant
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Interesting thread!  However, RAID5 may be irrelevant these days but the verdicts are not helping the asker.  Here is the bottom line: given that the asker only have 3 drives left, what is your recommendation?

Are you guys saying to do RAID1 with 2 drives and spare the 3rd drive instead of using RAID5 to utilize all 3 and have bigger capacity?  I will still go with RAID5 and my reason as stated above or we can recommend him to just buy new drives and maybe more quantity as well.
Andrew Hancock (VMware vExpert PRO / EE Fellow)VMware and Virtualization Consultant
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Not sure how many disks he has in RAID 5

He does not state in question

Destroy current Server and Rebuild current RAID as RAID 6 or RAID 10

And then create two virtual disks as OS and Data

Reinstall OS into C for OS and D for Data

The First virtual disk just needs enough space for OS
Abraham DeutschIT professional
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Thank all for your response and apologize for not yet responding I'm out of state and will be back tomorrow
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"What's your thought with RAID1?"
I'm a big fan of RAID1 for the small networks with which I deal.
I acknowledge the high cost (half of the space is lost), but that is often not a significant factor given how drive prices keep dropping.  I'm also assuming that the capacity of one large drive is adequate.  I recognize that this is not always realistic, but it has generally worked for me.

Performance can be very good with RAID1, even if a drive fails.

An extra drive configured as a hot spare will add an important layer of redundancy.  It doesn't avoid Andrew's concern about failure during rebuild, though.  I've not run into this but I can certainly see the potential.

Another benefit of RAID1 is the ease of doing data recovery if there are significant problems.  Either drive can be read as a single drive with a non-RAID controller.
Abraham DeutschIT professional
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Originally its 4 drives (the raid 5) each 300 GB which gives me 900 GB of space and one is failing.
8 hard drive slots
Base on the above posts

The Raid 1 can be ignored since its only a back up.

The Raid 5 should be replaces as the failure of one drive will cause the system to be very slow . (The server (in the bios) shows raid downgraded not sure is it means that is currently not ruing on raid 5 instead it dropped raid on this set)

Re that the drives are expensive.  If they are just for backup, you likely don't need 15k drives.  SAS drives can be reasonably priced, I believe i will get the speed of the less expensive drive, but will it not harm the other drives the fact that one drive hes lower speed?
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"The Raid 1 can be ignored since its only a back up."
If the array fails, you'll have some difficulty getting to the data on the RAID 5 array.  You wouldn't want to be fighting with that if you are needing the data.  Murphy's Law may bite you here.


How much space do you need?

I would consider purchasing a couple of 2T 7.2k SAS drives (under $100), and setting them up as RAID 1.  I'd create a primary partition of 200G for the OS and the remainder for the data.

Do a full backup of the OS and a restore to the 200G partition.  Copy your data from the RAID5 array to the data partition on the new drives.  If you don't care about the data (e.g. a new backup will be adequate) then you can skip the last step.

This should be a safe and cost-effective solution.
Abraham DeutschIT professional
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The simplest solution look to me suggested by arthurjb to buy new drives replace the bad drives, then wait for the raids to rebuild. Althght this should not be done on a server in general without first doing a backup as Andrew Hancock (VMware vExpert / EE MVE^2) sais RAID 5 may fail where a disk fails and been replaced and the RAID rebuild IO stress has caused another disk in the set fail during the rebuild resulting in a completely failed RAID set.

A vary critical point made by CompProbSolv and Wayne88 RAID5 The failure of one drive will cause the system to be very slow to read as it has to calculate the missing bit every time should be immediately replaced. But is not the case with raid 1 Adam Brown.

The idea of using less expensive drives suggested by CompProbSolv is a big help since it reduces the cost dramatically. I assume that this recommendation is because it is only a backup server, and as pointed out by arthurjb but not on a server in use since this would slow all drives to the speed of the slowest. Also I assume that it is not an issue having in one raid drives with different speeds.

In re Raid 5 over Raid 1

arthurjb Wayne88
RAID5 offers the best protection. Always use raid 5 stay away from RAID0 and RAID1

CompProbSolv PowerEdgeTech
Stay away from RAID 5 and stick with RAID 1 or RAID 10

Andrew Hancock (VMware vExpert / EE MVE^2)
RAID 5 is no longer considered usable in an enterprise environment because of just being able to handle a single drive failure and you should consider RAID 6 or RAID 10 based on performance or storage requirements.
Thank you all for you time a knowledge
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Thanks for getting back Abraham.  Cheers!

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