Software RAID to recover data from HW RAID

ocschwar · 02-25-2005, 09:11 PM

I inherited a RH9 (2.4.20) system that used an Adaptec SmartRaid V card with 7 SCSI drives in RAID 5 to store a /home partition. The card malfunctioned spectacularly and is en route to Adaptec, but in the meantime, I'd like to know if I can get the md driver to look at these disks, which are still sitting in a chain waiting for the to have a glance. I'm scared to write up a raidtab and let loose, because if the driver discovers the parity is wrong it might try to correct it wrongly, so I'd like to do it in a fail safe manner. It would also be really nice if the driver looked at the superblocks the Adaptec card left behind, and figured out from them what the drive order was (hence my desire for a fail safe here). I know somebody was doing a project to enable the md driver to look at superblocks from hardware RAIDS and figure out what to do with them. So, am I ringing any bells here? Has anyone tried this?

Matir · 02-25-2005, 09:21 PM

Unfortunately, as I understand it, it would be nearly impossible to make this work. Though the basic idea is the same with software and hardware raid, the exact layout of the blocks could quite well vary. While I welcome someone else to disagree with me and help you out, I'm afraid you won't have too much luck.

ocschwar · 02-25-2005, 09:24 PM

The industry standard is to put the superblock on the last 64k of each drive. Yes, there are exceptions, like the Dell PERC 320 (which put them on the first 64k), but they are exceptions. I know there was a project to reverse engineer superblocks and make them readable to the md driver, but if people here haven't seen it then I guess it may have fizzled out.

Matir · 02-25-2005, 09:58 PM

Well, I am far from a RAID expert: in fact, I've only used hardware raid once. Most of my RAID experience is software RAID.

ocschwar · 02-25-2005, 10:01 PM

This is the second time I am having this fight with a RAID controller card, and with that in mind I suggest you also not venture into hardware RAID territory. Without the ability to swap the drives to a different system for rescue, you can get hosed badly.

Matir · 02-25-2005, 10:05 PM

Well, of course, on the Enterprise level, hardware RAID can be quite useful for managing large file servers.