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Forum Discussion
Are drives mounted in Linux redundant?
As some of you will know I recently went through a disk array recovery (3 x 2.0 TB in Readynas NV). I sequentially cloned and drives and then used Linux to mount the set of clones to get my data. Thasnk to the people here who helped.
What I would like to know is when I mounted the 3 drives in Linux, were they mounted as a redundant set? Was Linux using the parity disk and would it have found any errors and repaired the data that I copied off ? If so, what part of Linux knows how to do this? LVM2?
Thanks for either an answer or a link to a good sourde for understanding this.
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If your ReadyNAS NV was running in Xraid mode,you can plug all the drives to Ubuntu system and execute below commands to get the data off from the disks
In a terminal window:
(1) sudo su (2) apt-get install fuseext2 (3) apt-get install lvm2 (4) modprobe fuse (5) vgscan (6) vgchange -ay c (7) fuseext2 -o ro -o sync_read /dev/c/c /mnt
if your the disks were created in Flex Raid,you need to use mdadm to start raid first
#mdadm --assemble /dev/md125 /dev/sd[abcd]3 --update=uuid #pvscan #vgscan #lvscan #vgchange -a y c #fuse-ext2 /dev/c/c /mnt
note:sd[abcd]3 means 3rd partition of each disk,you can execute command "cat /proc/partitions" to check on your Linux computer.
X-RAID for Sparc uses a dedicated parity disk. I don't think this disk is used at all if you're mounting the array in an ordinary Linux machine. The procedure is intended for data recovery attempts only (at your own risk, of course). So you do need all disks apart from the parity disk to be healthy for the recovery attempt to work smoothly.
The above only applies to our legacy Sparc systems. The procedures for all our other models (both X-RAID2 and Flex-RAID) and Flex-RAID on Sparc would use RAID.
With Flex-RAID the RAID would be used. However for Sparc Flex-RAID RAID-5 it may be a little more complicated, if I recall correctly.
If you'd rather not do the data recovery attempt yourself we do sell data recovery services that could be used to attempt the data recovery using a new unit. See e.g. ReadyNAS: Migrating disks from RAIDiator 4.1 or RAIDiator 5.3 to ReadyNAS OS 6 for more information.
My recovery is working out but I was having trouble understanding how the parity disk was being used when mounted by Linux and now I know why: it isn't used.
As it is time to move on from my original Infrant ReadyNAS NV. My thoughts are to move to a 2 disk system for the following reasons:
- $/TB is so low
- I always had more capacity than I needed with 3 installed disks
- every so often one must change out drives so there is a natural growth in installed size that should keep up to my needs
So then, what flavour of ReadyNAS RAID is the easiest to recover out of the NAS on a 2 disk system? or are they all the same for the 2 diskers?
The dedicated parity disk was only used by our Sparc systems the last of which was replaced in our product lineup back in November 2011.
With current models all RAID modes should be equally straightforward to recover. Though of course some RAID levels are better choices than others like they would be in any server e.g. a single RAID-0 volume spanning both disks is a bad idea as if either disk failed all data would be lost.I'd probably stick with the default X-RAID2 in e.g. a RN212 or RN422. It depends on what your needs are which way you'd want to go.
The RN422 has a display on the front and uses an Intel CPU. It'd be my preference.
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