RAID 5 Rebuild. What a terrible idea.

I've read similar stories, but this is my first time having to rebuild a RAID 5 array at home.

This is the most silly slow thankless task I have ever witnessed on a PC.
Going on 36 hours, for a 1.4TB array!

So why do I have a 1.4 TB RAID 5 array? it was to reuse 4 old 500GB drives which were once my photo storage in RAID 10 (striped and mirrored 1TB array, double speed and double copies)

When I moved up to larger drives, I housed the older 500gb drives in an external RAID box with 4 bays.
This was still a great idea, but the choice of RAID 5 maybe not so much.
If I gave up that 400GB for a mirrored RAID 1 array instead, my rebuild would have taken well under an hour.

Anyway, I actually had the 5th drive for a replacement, so I went RAID 5, and one drive died two days ago (click of death!!!) so I began the rebuild.


So it gets to 97% about 30 minutes ago, with just 24 minutes estimated remaining,.. then guess what? I get an error. It isn't going to finish!!!
My Redundant RAID 5 array is not going to rebuild, and despite the "redundancy" and the new drive, I won't be able to get any data off of it.

If I'd mirrored it (as I always have in the past) I would not need a working RAID to retrieve the data.

Fortunately this is a copy of a copy.. but some might have used a RAID 5 thinking they were covered.

This will be my last use of RAID 5

What controller do you have? Takes me 1-2 hrs to rebuild bigger arrays, but that's usually involves a higher end Dell PERC (rebranded LSI) controller.

Oh yeah, this is a very cheap home project controller.
It's a SIL3132 controller that came with the raid box.
The box is a "Rosewill" (Newegg home brand) that's a steal @ $119.99 with the controller card. It will turn one esata port into a 4 drive controller via the built in repeater.

So for a little over $100.00 you can add four drives to one esata port.
I find the whole kit actually pretty impressive, especially for what it costs. But this iteration of RAID 5 is pants.


FYI, I closed the error dialog and RAID utility that was managing the array with task manager, rebooted, and lo and behold, I have my rebuilt array! ...despite what the utility says

I'll make sure there's nothing I need to copy over and then likely obliterate the array.

Yeah, from my experience RAID5 is not a good idea unless you're willing to spend the money on a good controller or willing to put time into getting an older used controller from a server and making sure it works in your machine.

DiMAn0684 wrote in post #15800018
Yeah, from my experience RAID5 is not a good idea unless you're willing to spend the money on a good controller or willing to put time into getting an older used controller from a server and making sure it works in your machine.

Yeah cheaping out on a RAID5 controller is just asking for trouble.

RAID is never a substitute for a backup.

Parity-based RAID is just a way to gang together spindles to get more capacity while attempting to mediate the mathematical fact that if you have 5 devices of MTBF "X" the MTBF of the entire set if you cannot lose any of them is in fact X/5!

I've seen a 11TB RAID5 rebuild (replace hot-spare) in less than a couple of hours... Although this was on a enterprise grade SAN

The purpose on this SAN was to store MANY days of data continuously... at the point which it gets full, that data begins to re-write over the oldest data. For this situation, a true backup is not required, but losing all data is quite a failure. The SAN has successfully overcome a number of drive failures and no data has yet to be lost; although we've yet to experience 2 failed drives at the same time

drvnbysound wrote in post #15804001
I've seen a 11TB RAID5 rebuild (replace hot-spare) in less than a couple of hours... Although this was on a enterprise grade SAN

The purpose on this SAN was to store MANY days of data continuously... at the point which it gets full, that data begins to re-write over the oldest data. For this situation, a true backup is not required, but losing all data is quite a failure. The SAN has successfully overcome a number of drive failures and no data has yet to be lost; although we've yet to experience 2 failed drives at the same time

Why no RAID6?

I don't think RAID 6 was very prevalent during the time of installation (years ago)... it basically wasn't an option at the time or wasn't available via the the hardware we have.

I had similar experiences with a RAID5 array and a Adaptec SATA controller.

Now im onto ZFS and nothing less than RAIDZ2 (ZFS RAID6). Much faster rebuilds, even with a full array. Less than full, it only has to rebuild the data, not the entire disk. Half capacity usage means half the rebuild time. Nevermind it warns you far sooner that a disk is having issues. Or that theres a bad cable, controller, etc. Theres a million benefits to it, over even good hardware RAID controllers.

Once you go ZFS its hard to even think about downgrading and going back to hardware RAID.

I must say I've never hung around long enough for a RAID to rebuild - I used to do break / fix for HP servers and a lot of the calls involved popping out the dead drive and putting in a new one.