RAID5 recovery on Macintosh - RAID parameters

Discussions on using the professional data recovery program R-STUDIO for RAID re-construction, NAS recovery, and recovery of various disk and volume managers: Windows storage spaces, Apple volumes, and Linux Logical Volume Manager.
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RAID5 recovery on Macintosh - RAID parameters

Post by bvoight » Thu Sep 12, 2013 9:25 am

Hi all -

Couple weeks back I had what appeared to be a 2 disk failure on my RAID5 6 disk (2Tb each) set-up disk array on my PROMISE Pegasus R6 drive (connected to my Macmini via thunderbolt).

There does not appear to be mechanical failure of the drives, so I proceeded to attempt data recovery via imaging the drives and rebuilding the virtual array using R-Studio.

Each of the drives appear to have imaged OK (took 6 days overall).

Based on a previous system dump using the PROMIS disk util of the array when I was trying to debug it, I think (though I am not sure) of the following RAID parameters:

Disk Order: I'm prettys sure I have the order of the array correct (confirmed via serial number)
Stripe Size: 128 kb
Block Order: "Right asymmetric" is what was given in the subsystem info check (assume that is analogous to Right Asynchronous)

Offset: Unsure

I set of a virtual array with 6 rows, 128kb block size, right asynchronous, and 6 rows. Each image has an offset set to "0 sectors"

I then begun a scan, and Rstudio certainly found a file structure and data vaguely representing what I recall was on the drive. (the file system is NFS+)

When I look carefully at some of the files, however, the data contained looks scrambled: files contain some correct data but do not start at the beginning of what I remember the files to be (starts mid-line), files I which should contain some expected content (e.g. README) appear to contain data that belong to other files, etc.

Seems to me like I've either got the offset wrong or some other RAID parameter incorrect. Does this seems like the correct diagnosis?

Given that this is connected through hardware which I can only connect to a mac (and thus using a tool like ReclaiMe is not possible), how do I go about the job of identifying the proper RAID parameters?

I'm currently trying to work through the "Finding RAID parameters" walkthrough (started searching for the Master boot record hex on disk images) though that search is taking a very long time (24 hours still hasn't found anything, and only 1/2 though one drive image).

If I have to play the game of trying a couple of parameters, given that scanning take a long time to perform (on the entire drive), is it reasonable quickly iterate through possible likely configurations until I come to one which seems 'right'?

Thanks and appreciate any advice.

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Re: RAID5 recovery on Macintosh - RAID parameters

Post by Alt » Sat Sep 14, 2013 7:57 am

First, and the most important question:
Are you sure that you have 2 failed disks? If yes, you can't recover data, as RAID5 can tolerate loss of 1 disk only.

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Re: RAID5 recovery on Macintosh - RAID parameters

Post by bvoight » Mon Sep 16, 2013 8:53 am

Hi there -

When this issue came up, it appeared that two drives were being read by the array as non-functional, though neither of the drives seemed to have an obvious mechanical failure (they both imaged OK, and recovery is proceeding at pace below).

My hunch is that something went horribly wrong with the controller.

After some tinkering last week, I did manage to figure out the issue I was having last week (turned out to be that two of the drives were flipped, so I had the order mis-specified).

For anyone out there that ends up needing to know these things, at least on my default RAID5 set-up with the Pegasus R6:
(1) If you have it, you can obtain a subsystem report from the PROMISE utility which gives some details (though not all) about parameters, including block size (=128kb in my case) and the structure of the RAID (in my case, Right asymmetrical = Right Asynchronous). The disk order should also potentially be clear from that file (though I thought I had written down the order and serial numbers correctly, and got stuck here with two drives being flipped around).
(2) Offset = 0
(3) rows = 6

This set up worked and discovery everything fairly clearly, and it appears (cautious optimism) that most if not everything is recoverable and I'm working that through as I write.



Re: RAID5 recovery on Macintosh - RAID parameters

Post by dhinostroza » Sat Dec 12, 2020 1:47 pm

To avoid mixing up the position of the disks I use a permanent marker to write the order of the disks on the top side of the drive from top to bottom (1, 2, 3, and so on). Or from left to right, depending on the RAID enclosure. If a drive fails I place an X on it before removing it entirely.

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Re: RAID5 recovery on Macintosh - RAID parameters

Post by RForce » Mon Dec 14, 2020 9:00 am

Good job. One thing you should consider is that if 2 drives reported as failed, it is entirely possible that one failed a considerable amount of time before the other. So, best practice would be to play with the various RAID combinations with either of these drives offline and then compare the results. Test a few of the most recently created/edited files to confirm that they are 100% healthy.

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