Re: Rebuilding an array with a corrupt disk.

[David Greaves <david@dgreaves.com>]

Sean Hildebrand wrote:
> I had a batch of disks go bad in my array, and have swapped in new disks.
> 
> My array is a five disk RAID5, each 750GB. Currently I have four disks
> operational within the array, so the array is functionally a RAID0.
> Rebuilds have gone fine, except for the latest disk, which I've tried
> four times.
> 
> At 74% into the rebuild, mdadm drops /dev/sdd1 (The spare being
> synced) and /dev/sda1 (A synced disk active in the array.) due to a
> read error on /dev/sda1. Checking smartctl, there have been 43 read
> errors on the disk, and they occur in groups.

You have 2 faulty drives.

Pounding on them will only make things worse.

Get 2 new drives and use ddrescue to copy /dev/sda to a new drive and replace
/dev/sda. Then add your second new drive.

> The array contents have been modifed since the removal of the older
> disks - So only the four currently-operational disks are synced.

> Fscking the array also has issues past the halfway mark - Namely, when
> it gets to a certain point, /dev/sda1 is dropped from the array and
> fsck begins spitting out inode read errors.
Well, once sda is gone you're reading garbage if the array even stays up.

> Are there any safe ways to remedy my problem? Resizing the array from
> five disks to four and then removing /dev/sda1 is impossible, as for
> the array to be resized, error free reads of /dev/sda1 would be
> necessary, no?
It depends how well ddrescue does at reading /dev/sda.

The sooner you do it the more chance you have.

David