RAID5 failure: 2 bad HDD's at the same time

[CapLeaker]

Re: RAID5 failure: 2 bad HDD's at the same time

this is why for large arrays, raid 6 is a better idea

that is what I am aiming for, something where 2 drives can fail. Anyone tried the SHR2 from Synology?

[CapLeaker]

Re: RAID5 failure: 2 bad HDD's at the same time

You _NEVER EVER EVER_ do that!
If a Drive in a RAID Array fails, you build a new one and copy the content from the old to the new one as long as it works. Start with the most important things.

Also RAID is NOT a replacement for the BACKUP!

So all you can do right now is to clone the drives and hope you have everything you need, then rebuild the RAID with the new drives....

Interesting... So you are saying to clone the bad HDD's in the RAID 5 array with clonezilla to a new drive and put it back into the array? I thought the array knows the HDD by serial number or something, so it would detect it as a "new" drive?

No, I've lost nothing important and that is a good thing. I do have a few offline HDDs. Some of the stuff on the RAID array was so old, it gives me a chance to clean up my file storage. Rather than copying everything and deleting the stuff no longer wanted, I just revesed it by copying only the stuff I want. This gives me more space.

[Stefan Payne]

Re: RAID5 failure: 2 bad HDD's at the same time

Well, I guess I ran out of luck and shit hit the fan all right at home, ugh!
I am running a WD PR4100 16TB NAS. All was good until I noticed some slow file transfer occasionally. Done a HDD test and drive 2 failed. O.K. no problem, order new drive, replace drive and rebuild RAID5. Easy, right? Well not so fast. Wouldn't you suppose, the drive 3 failed, during the half way mark of rebuilding the RAID5 array on drive 2?

You _NEVER EVER EVER_ do that!
If a Drive in a RAID Array fails, you build a new one and copy the content from the old to the new one as long as it works. Start with the most important things.

Also RAID is NOT a replacement for the BACKUP!

So all you can do right now is to clone the drives and hope you have everything you need, then rebuild the RAID with the new drives....

[diif]

Re: RAID5 failure: 2 bad HDD's at the same time

This is why RAID IS NOT BACKUP.

[Uranium-235]

Re: RAID5 failure: 2 bad HDD's at the same time

this is why for large arrays, raid 6 is a better idea

[Curious.George]

Re: RAID5 failure: 2 bad HDD's at the same time

therefore, i prefer to diy my own nas and thus pick drives with different platter density technologies and different number of heads etc. so they would fail at different times instead.

They still have many things in common: the hardware/software that's implementing the array, power supply, thermal experience, software that is accessing the array, etc.

I prefer to trade robustness for convenience -- I only spin up a drive when I'm accessing its contents. If that content is munged, then I have to consider how much of the other content may be at risk. Or, if the box that I'm using to access that drive may, instead, be the culprit.

[Software/firmware/clients/apps/PEBKAC have been known to be buggy]

As I don't expect to encounter problems, when/if I do, it gives me a moment to think about what's happening before I propagate a failure (to other copies of the data).

[CapLeaker]

Re: RAID5 failure: 2 bad HDD's at the same time

Well, drive 2 is FUBAR. Won't read from it period. Not sure why Drive 3 has some bad sectors and I was able to get the important stuff off the Raid5. So that is good. However I am not able to recover the whole Raid array. But that is o.k. I kept too much junk anyway.

[eccerr0r]

Re: RAID5 failure: 2 bad HDD's at the same time

I've been able to successfully reassemble my Linux md-RAID5 arrays that were destroyed by two disk failures, but there's no guarantee that the data I pull off is accurate. However I was able to get a good portion of the data off after the failure.

Which reminds me, I need to backup my array again soon...

[ChaosLegionnaire]

Re: RAID5 failure: 2 bad HDD's at the same time

thats why i dont buy nas boxes off the shelf. they are typically composed of a homogeneous set of drives so this means that the drives have a tendency to all fail at the same time! talk about very convenient planned obsolescence there! im sure the companies that make these nas boxes couldnt care less either if it means more buying and more money!

therefore, i prefer to diy my own nas and thus pick drives with different platter density technologies and different number of heads etc. so they would fail at different times instead.

do what eccerror said. for me, i fire up linux, pull the smart data, see how many pending, uncorrectable and reallocated sectors there are and run gnu ddrescue to pull as much data off the bad drive as possible if its still acessible and not bricked in which case the drive is totally unaccessible and undetectable neither by the bios nor os.

if the drive is bricked and the data is critical, send it to a data recovery company. the fee could cost thousands of dollars for the recovery.

[eccerr0r]

Re: RAID5 failure: 2 bad HDD's at the same time

As always RAID is not a backup.
Question is, how bad are the drives. If you pull them up on their own on a PC (DON'T WRITE TO THEM!) can you at least read a few bytes? SMART information?

If you have two drives completely dead, you're probably SOL. If just one is dead and one has a few bad sectors, depending on your NAS firmware you may be able to recover something...unfortunately I don't have any experience with WD's RAID, just Linux mdraid...

[Curious.George]

Re: RAID5 failure: 2 bad HDD's at the same time

Well, I guess I ran out of luck and shit hit the fan all right at home, ugh!
I am running a WD PR4100 16TB NAS. All was good until I noticed some slow file transfer occasionally. Done a HDD test and drive 2 failed. O.K. no problem, order new drive, replace drive and rebuild RAID5. Easy, right? Well not so fast. Wouldn't you suppose, the drive 3 failed, during the half way mark of rebuilding the RAID5 array on drive 2?

This is a known problem with RAID -- esp with larger drives! The time it takes to rebuild the array represents a sizeable window in which a second failure can eat your lunch...

Of course, the "cost" (window of vulnerability) of rebuilding the failed drive will vary (e.g., RAID5 being more expensive than RAID1).

[CapLeaker]

Well, I guess I ran out of luck and shit hit the fan all right at home, ugh!
I am running a WD PR4100 16TB NAS. All was good until I noticed some slow file transfer occasionally. Done a HDD test and drive 2 failed. O.K. no problem, order new drive, replace drive and rebuild RAID5. Easy, right? Well not so fast. Wouldn't you suppose, the drive 3 failed, during the half way mark of rebuilding the RAID5 array on drive 2?

Question is: How do I recover all the files or recover the RAID?