Re: [LUG] OT: Reading single RAID 1 HD from failed array.

[Julian Hall <linux@xxxxxxxxxxxx>]

Sorry that should be /dev/sdc for the real device.. /dev/sdc3 is where the data is.

On 08/06/17 16:02, Julian Hall wrote:

Hi Simon,

I took the working drive out of the NAS and put it in a USB caddy. Since when I have been trying for a few hours to get it to mount in Linux - I keep going round in circles. From what I can make out Linux has created a software RAID device, /dev/md2 which is busy, and mapped the real device to that; stopping it does nothing helpful. The drive itself is - according to GParted - /dev/sd3. As it is a RAID1 volume with all the data intact - I could see it all in Synology's Disk Station Manager (DSM) software, what would happen if I just took the RAID flag off in GParted?

Kind regards,

Julian

On 04/06/17 20:37, Simon Avery wrote:

Hi again,

You could try mounting the non-dead drive onto your linux machine - could work and shouldn't break if it it's not already. (If you just mount it, but mount read-only to be sure)

But I don't know what crazy tricks Synology do with their software - so it's not really a linux issue, even if their boxes run stock linux without any mods, which seems unlikely.Â

Good luck with it. Hope you had a back up. (Repeat the mantra: RAID is not a backup...)Â

On 4 June 2017 at 19:44, Julian Hall <linux@xxxxxxxxxxxx> wrote:

Hi Simon,

I understand that's how it's /supposed/ to work, and indeed the last time a single disk failed in the same NAS that is exactly what happened. However this time I was able to access the surviving disk once only, and not since. The Synology software says the array is 'degraded'. I tried repairing it as per the Synology support pages and it /said/ both disks were now normal but still refused to mount the volume. Then when I restarted the NAS the troubled disk (no. 2) disappeared and now only no. 1 displays.

That's when I emailed for help. I suspect I will have to wait until the new HD on order arrives and see what happens then.

Kind regards,

Julian

On 04/06/17 18:41, Simon Avery wrote:

Hi Julian,

The whole point of RAID 1 is that work continues as normal in a single HDD failure.

Synology device should continue working with one dead drive, if there are two and it's RAID 1. Read their support pages.

A lot depends on the software used to make the raid. mdadm is the most common linux software, and each drive can be mounted separately as a straight device, but hardware and fakeraid (BIOS software raid) can be wildly different and it's hard to know without more details. Not all RAID setups are equal, y'see.

HTH

On 3 June 2017 at 23:05, Julian Hall <linux@xxxxxxxxxxxx> wrote:

Hi All,

One of the two HDs in my Synology DS212j (RAID 1 array) has packed in, and the last time this happened I was still able to read the data on the other surviving disk. This time I was able to access it /once/ but not since - it refuses to mount at all. A friend mentioned he was able to read from a single RAID 1 disk after a crash in Linux but couldn't remember how; we've searched the forums all afternoon without success.

Any advice gratefully received.

Kind regards,

Julian

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