Question Raid 5 - HD failure + URE

[samik83]

Hi,

Question about RAID 5. I got a Buffalo NAS a few days ago that's setup up as raid 5. Only afterwards I started reading about the negatives of raid5 and how people are moving away from it. What I've read is the failure rate is fairly high during a drive re-builds, since bad sectors or URE's aren't that uncommon, especially when running multi TB arrays.


So, my question is, is rebuilding the array the same as taking a backup copy when there's a failed drive. If an URE can cause you to lose all your data during a rebuild, will a simple backup with the remaining drives only result in the loss of a file or two that's caused by the URE?

Hope I'm making sense here. If not, ask and I'll try to clarify.

 

[kanewolf]

Rebuilding a RAID 5 requires every used sector of the "good" drives be read to create the missing data to write to the new drive. Data loss can happen on rebuild. That is why critical data can't be stored in one place. You should have three copies of critical data, including one off-site copy.

 

[samik83]

Yes, I understand that is the case when re-building, you need everything from the remaining drives.
However, you should be able to access the data with one failed drive. Correct?
So I want to know if I can just copy the data from the remaining good drives (as a backup in case of URE's), before attempting to rebuild?
Or does any URE's in the remaining drives prevent you from accessing any data?

 

[kanewolf]

Yes, I understand that is the case when re-building, you need everything from the remaining drives.
However, you should be able to access the data with one failed drive. Correct?
So I want to know if I can just copy the data from the remaining good drives (as a backup in case of URE's), before attempting to rebuild?
Or does any URE's in the remaining drives prevent you from accessing any data?

Yes. The arrays will report "degraded" but you can still access the data. If there are unreported errors, then you could have files that will fail to copy or be corrupted in your backup.

 

[USAFRet]

Remove one drive from a RAID 5, the data should still be accessible and copyable to some other space.

And having that second copy is strongly recommended before, during, and after the rebuild.

One of the problems with a RAID 5 and 'large' drives is...if you have 3-4-5 drives of the same type, bought at the same time....if one fails, the others may not be far behind.
And the rebuild may take many hours. Stressing the drives even more.

I have a 4 drive RAID 5 in my NAS. 4 x 4TB.
Rebuilding a RAID 5 with approx 6 TB consumed space takes about 6-7 hours of constant banging on those drives.

I'm in the planning stages of undoing that RAID 5. It was mostly just an experiment.

 

[samik83]

Ok., thanks for the answers. A lot of people keep saying R5 is dead and you should not use it because of the risk in re-building. Started making me paranoid since I'm new to raids.

I'm mainly using it as a backup for my photos and home videos, so I have another copy always at hand.
The raid part just comes in handy for my fairly large movie collection. I didn't want to invest in another dedicated system just to back them up, so I thought this is the next best thing and I get media server in the same package. Not a huge deal if I lose them, but it's nice to have some redundancy for decades worth of movie collecting.

 

[USAFRet]

The only protection the RAID 5 gives is physical drive fail, of a single drive.

 

[digitalgriffin]

Hi,

Question about RAID 5. I got a Buffalo NAS a few days ago that's setup up as raid 5. Only afterwards I started reading about the negatives of raid5 and how people are moving away from it. What I've read is the failure rate is fairly high during a drive re-builds, since bad sectors or URE's aren't that uncommon, especially when running multi TB arrays.


So, my question is, is rebuilding the array the same as taking a backup copy when there's a failed drive. If an URE can cause you to lose all your data during a rebuild, will a simple backup with the remaining drives only result in the loss of a file or two that's caused by the URE?

Hope I'm making sense here. If not, ask and I'll try to clarify.

This is why raid 6 was was invented. But raid 0+1 is pretty good. When rebuilding a 0 + 1 your reading data from one drive not 2, 3, or 4 trying to rebuild it. And to be honest most NAS 1gb network connections are slower than raid 5 anyway. So the benefits of spanning are moot.

Buy NAS drives (wd red). They cost more but are more reliable.

I have a 4tb external as my network backup. And two portables which I hand back up family photos and movies on as a secondary. I run them on alternating years.