I know how RAID work and prevent data lost from disks failures. I want to know is possible way/how easy to recover data from unfunctioned remaining RAID disks due to RAID controller failure or whole system failure. Can I even simply attach one of the RAID 1 disk to the desktop system and read as simple as USB disk? I know getting data from the other RAID types won’t be that simple but is there a way without building the whole RAID system again. Thanks.
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I’d stay away from hardware RAID controllers. If they fail you’re gonna have a hard time. Learned that the hard way. With a software RAID you can do what you proposed. Just put the disk in another system and use it there.
Seconded. Software RAID is much easier to recover from.
I’m going to give you the benefit of the doubt and assume what you said was simply confusing, but not wrong.
So just to be clear if your raid array fails, and you’re using software raid, you can plug all of the disks into a new machine and use it there. But you can’t just take a single disk out of a raid 5 array, for example, and plug it in and use it as a normal USB hard drive that just had some of the files on it, or something. Even if you built the array using soft-raid.
No, they mean that if the controller fails, you have to get a compatible controller, not just any controller. And that usually means getting another of the exact same controller. Hopefully they’re still available to buy somewhere. And hopefully it’s got a matching firmware version.
But if you’re using mdraid? Yeah just slap those drives on any disk controller and bring it up in the OS, no problem.
- RAID is never a replacement for backups.
- Never work directly with a surviving disk, clone it and work with the cloned drive.
- Are you sure you can’t rebuild the RAID? That really is the best solution in many cases.
- If a RAID failure is within tolerance (1 drive in a RAID5 array) then it should still be operational. Make a backup before rebuilding if you don’t have one already.
- If more disks are gone than that then don’t count on recovering all data even with data recovery tools.
The OP made clear it was a controller failure or entire system (I read hardware here) failure. Which does complicate things somewhat.
Yeah, if there’s a full system failure without any backups and no option to get the system operational again then I would land in clone the drives before trying to restore data from them.
For recovering hardware RAID: most guaranteed success is going to be a compatible controller with a similar enough firmware version. You might be able to find software that can stitch images back together, but that’s a long shot and requires a ton of disk space (which you might not have if it’s your biggest server)
I’ve used dozens of LSI-based RAID controllers in Dell servers (of both PERC and LSI name brand) for both work and homelab, and they usually recover the old array to the new controller pretty well, and also generally have a much lower failure rate than the drives themselves (I find myself replacing the cache battery more often than the controller itself)
Only twice out of the handful of times I went to a RAID controller from a different generation
- first time from a mobi failed R815 (PERC H700) physically moving the disks to an R820 (PERC H710, might’ve been an H710P) and they were able to foreign import easily
- Second time on homelab I went from an H710 mini mono to an H730P full size in the same chassis (don’t do that, it was a bad idea), but aside from iDRAC being very pissed off, the card ran for years with the same RAID-1 array imported.
As others have pointed out, this is where backups come into play. If you have to replace the server with one from a different generation, you run the risk that the drives won’t import. At that point, you’d have to sanitize the super block of the array and re-initialize it as a new array, then restore from backup. Now, the array might be just fine and you never notice a difference (like my users that had to replace a failed R815 with an 820), but the result pattern is really to the extremes of work or fault with no in between.
Standalone RAID controllers are usually pretty resilient and fail less often than disks, but they are very much NOT infallible as you are correct to assess. The advantage to software systems like mdadm, ZFS, and Ceph is that it removed the precise hardware compatibility requirements, but by no means does it remove the software compatible requirements - you’ll still have to do your research and make sure the new version is compatible with the old format, or make sure it’s the same version.
All that’s said, I don’t trust embedded motherboard RAIDs to the same degree that I trust standalone controllers. A friend of mine about 8-10 years ago ran a RAID-0 on a laptop that got it’s super block borked when we tried to firmware update the SSDs - stopped detecting the array at all. We did manage to recover data, but it needed multiple times the raw amount of storage to do so.
- we made byte images of both disks in ddrescue to a server that had enough spare disk space
- found a software package that could stitch together images with broken super blocks if we knew the order the disks were in (we did), which wrote a new byte images back to the server
- copied the result again and turned it into a KVM VM to network attach and copy the data off (we could have loop mounted the disk to an SMB share and been done, but it was more fun and rewarding to boot the recovered OS afterwards as kind of a TAKE THAT LENOVO…we were younger)
- took in total a bit over 3TB to recover the 2x500GB disks to a usable state - and took about a week of combined machine and human time to engineer and cook, during which my friend opted to rebuild his laptop clean after we had images captured - to one disk windows, one disk Linux, not RAID-0 this time :P
I’m sure I’ve seen paid software that will detect and read data from several popular hardware controllers. Maybe there’s something free that can do the same.
For the future, I’d say that with modern copy on write filesystems, so long as you don’t mind the long rebuild on power failures, software raid is fine for most people.
I found this, which seems to be someone trying to do something similar with a drive array built with an Intel raid controller
Note, they are using drive images, you should be too.
Keep multiple reliable (and tested) backups, if something fails restore a backup.
Don’t rely on any storage, RAID or anything else to be recoverable when something goes wrong.
recover data from unfunctioned remaining RAID disks due to RAID controller failure
In this case, you need a new RAID controller of similar type.
Can I even simply attach one of the RAID 1 disk to the desktop system
No. One disk out of a RAID array is different from a normal disk.
Recovery becomes easy if you do not use a hardware RAID controller, but a ZFS software RAID instead. It does nearly all automatically. But you need to do a little more reading tutorials for the first setup.
RAID is more likely to fail than a single disk. You have the chance of single-disk failure, multiplied by the number of disks, plus the chance of controller failure.
RAID 1 and RAID 5 protect against that by sharing data across multiple disks, so you can re-create a failed drive, but failure of the controller may be unrecoverable, depending on availability of new, exact-same controller. With failure of 1 disk in RAID 1, you should be able to use the array ‘degraded,’ as long as your controller still works. Depending on how the controller works, that disk may or may not be recognizable to another system without the controller.
RAID 1 disks are not just 2 copies of normal disks. Example: I use software RAID 1, and if I take one of the drives to another system, that system recognizes it as a RAID disk and creates a single-disk, degraded RAID array with it. I can mount the array, but if I try to mount the single disk directly, I get filesystem errors.
Are there differences in the context of failure, when using a controller vs software raid with mdadm?
With software raid, there is no controller to fail.
Well, that’s not strictly true, because you still have a SATA/SAS controller, HBA, backplane, or whatever, but they’re more easily replaceable. (Unless it’s integrated in the motherboard, but then it’s not a separate component to fail.)
Software RAID is generally better in every way, also no hardware to fail.
I’ve never been a big fan of RAID for this reason… but I’ve also never had enough mission critical data that I couldn’t just store hard copy backups.
That being said… let me ask you this:
Is there a better way than RAID for data preservation/redundancy?
Just for drive redundancy it’s awesome. One drive fails you just pull it out, put in a new one and let the array rebuild. I guess the upside of hardware RAID is that some even allow you to swap a disk without powering down. Either way, you have minimal downtime.
I guess a better way would be to have multiple servers. Though with features like checksums in BTRFS I guess a RAID is still better because it can protect against bitrot. And with directly connected systems in a RAID it is generally easier to ensure consistency.
Yeah, that’s generally my consensus as well. Just curious if someone had a better way that maybe I didn’t know about.
A tool I’ve actually found way more useful than actual raid is snapraid.
It just makes a giant parity file which can be used to validate, repair, and/or restore your data in the array without needing to rely on any hardware or filesystem magic. The validation bit being a big deal, because I can scrub all the data in the array and it’ll happily tell me if something funky has happened.
It’s been super useful on my NAS, where it’s the only thing standing between my pile of random drives and data loss.
There’s a very long list of caveats as to why this may not be the right choice for any particular use case, but for someone wanting to keep their picture and linux iso collection somewhat protected (use a 321 backup strategy, for the love of god), it’s a fairly viable option.
Very cool, this is actually the sort of thing I was interested in. I’m looking at building a fairly heavy NAS box before long and I’d love to not have to deal with the expense of a full raid setup.
For stuff like shows/movies, how do they perform after recovery?
I mean, recovery from parity data is how all of this works, this just doesn’t require you to have a controller, use a specific filesystem, have matching sized drives or anything else. Recovery is mostly like any other raid option I’ve ever used.
The only drawback is that the parity data is mostly equivalent in size to the actual data you’re making parity data of, and you need to keep a couple copies of indexes since if you lose the index or the parity data, no recovery for you.
In my case, I didn’t care: I’m using the oldest drives I’ve got as the parity drives, and the newer, larger drives for the data.
If i were doing the build now and not 5 years ago, I might pick a different solution but there’s something to be said for an option that’s dead simple (looking at you, zfs) and likely to be reliable because it’s not doing anything fancy (looking at you, btrfs).
From a usage (not technical) standpoint, the most equivalent commercial/prefabbed solution would probably be something like unraid.
