"Reconstructing RAID"

Post #302695913 by Lem on Tuesday 4th of September 2012 05:07:31 AM

Full Discussion: Reconstructing RAID
From what I've been reading about those ShareSpace devices, there should be an LVM2 volume, indeed, on top of the raid. So you should find it, and then mount it. If things are like that, of course you cannot mount the raid volume itself, because it doesn't have a filesystem on it. But you didn't find the lvm2 volume, when running vgscan, so I don't have good feelings... Smilie

Since you've used --force to reassemble the raid (instead of only --run), now the raid is active, but it could nonetheless be corrupted:

(from mdadm manual)
Quote:
-f, --force
Assemble the array even if the metadata on some devices appears to be out-of-date.
If mdadm cannot find enough working devices to start the array, but can find some
devices that are recorded as having failed, then it will mark those devices as
working so that the array can be started. An array which requires --force to be
started may contain data corruption. Use it carefully.

-R, --run
Attempt to start the array even if fewer drives were given than were present last
time the array was active. Normally if not all the expected drives are found and
--scan is not used, then the array will be assembled but not started. With --run
an attempt will be made to start it anyway.
Let's made another attempt, manually inspecting the beginning of /dev/md2:

Code:
# dd if=/dev/md2 bs=512 count=255 skip=1 of=/tmp/md2lvm
# less /tmp/md2lvm

(Better than less, use a text editor of your choice).

Among binary data, do you see some LVM metadata declarations? Can you find the most recent one? Or there's nothing useful?
--
Bye
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raidreconf(8)						      System Manager's Manual						     raidreconf(8)

NAME
raidreconf - reconfigure RAID arrays SYNOPSIS
raidreconf -h {--help} - or - raidreconf -V {--version} - or - raidreconf -o oldraidtab -n newraidtab -m /dev/md? - or - raidreconf -i /dev/sd?? -n newraidtab -m /dev/md? - or - raidreconf -n newraidtab -m /dev/md? -e /dev/sd?? WARNING
You should back up all data BEFORE any attempt is made to reconfigure a RAID device. YOU HAVE BEEN WARNED. The author will give you no guarantee whatsoever, that this program works in any specific way at all. It may well destroy all data on any device connected directly, indirectly, or not at all, to any system this software is used on. Please use this stuff with care, if you decide to use it at all. Ok, that said, let's see how to actually use it :-) DESCRIPTION
raidreconf will read two raidtab files, an old one, and a new one. It will then re-build your old array to match the configuration for the new array, while retaining all data possible. It can also be used to import a single block-device into a RAID array (using more block devices), or export a RAID array to a single block- device. raidreconf can, of course, only retain your original data if you grow the configuration. If you shrink the configuration from say, P bytes to Q bytes, raidreconf will retain the first Q bytes of your original data, but everything from Q bytes to the end of the old array (to P bytes) will be lost. Currently raidreconf can grow and shrink RAID-0 and RAID-5 arrays, and import non-RAID devices into a new RAID-0 or RAID-5. The whole purpose of raidreconf is to be able to add disks to an existing array, or convert it to a new type (eg. RAID-0 to RAID-5) without losing data. raidreconf will move the existing data around on your array, to match the layout of the new array. OPTIONS
-h {--help} Raidreconf will print a short help message, and exit. -V {--verbose} Raidreconf will print it's version information, and exit. -o {--old} oldraidtab Specifies the path name of the old (current) raidtab. NOTE: raidreconf performs some tests to ensure that this configuration file matches the raid superblocks stored on the disk, but there may be scenarios where the two are in conflict, but aren't detected as such. Be very careful to specify this file properly. -n {--new} newraidtab Specifies the path name of the new raidtab. After raidreconf finishes, copy the newraidtab to the oldraidtab location, as raidreconf doesn't perform this (potentially dangerous) operation. -m {--mddev} /dev/md? Specifies the name of the raid array to modify. -i {--import} /dev/sd?? Specifies the name of the device to import from. -e {--export} /dev/sd?? Specifies the name of the device to export to. BUGS
Perhaps many. Well, the basic RAID-0 growth, shrink and import algorithms seem to work, but there are lots and lots of consistency checks and graceful error handling missing. The RAID-5 algorithms are simplistic, with little optimization other than that provided by the buffer layer. Conversions between non-RAID, RAID-0, and RAID-5 all *seem* to work, but there may be some bugs left yet. If an error occurs during reconfiguration, a power failure for example, restore from backup (you DID make a backup, right?), and try again. Although RAID-4 is not supported, and almost no one uses it, it would be almost trivial to add. REPORTING BUGS
Since this is highly experimental software, there are a number of known bugs already. The author would of course like to know about bugs, but at this stage in development you shouldn't waste too much of your time trying to hunt them down. They're probably known, and maybe already fixed in the author's tree. Report bugs to <bugs@oss.connex.com>. ????? AUTHOR
raidreconf was written in 1999 by Jakob Oestergaard <jakob@ostenfeld.dk> The RAID-5 routines were written by Daniel S. Cox in 2001 <dcox@connex.com> SEE ALSO
mkraid(8), raidtab(5), raidstart(8), raidhotadd(8), raidhotremove(8), raidstop(8) raidreconf(8)

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