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LINUX-L  2017

LINUX-L 2017

Subject:

Re: RAID management

From:

Eben King <[log in to unmask]>

Reply-To:

Platform Independent Linux List! <[log in to unmask]>

Date:

Sun, 3 Sep 2017 16:05:04 -0400

Content-Type:

text/plain

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text/plain (52 lines)

 > On 09/03/2017 02:59 PM, Eben King wrote:
 >> I have a RAID-1 setup (2x1 TB) that I use for media storage.  I want to
 >> migrate to a new(er) set of disks....

 >> One disk was copied successfully, at
 >> least about 2/3 of it.  Then something crapped out and I had to resume.
 >> Assuming I got if= and of= correct in dd, the rest should be copied
 >> successfully too.  The other, I know I screwed up on.
 >>
 >> So, what's the way that puts the least stress on the drives to expand the
 >> RAID from one disk to two?  Also, what's a more, er, "user-tolerant" way
 >> to duplicate disks that can be resumed?
 >>
 >

On 09/03/17 15:47, William A. B. Maloney wrote:
> This is not a definitive answer, to be sure, but I would look at *rsync* to 
> do the data-copying. If you're starting with a blank target disk, it will 
> copy everything over. If, however, you're starting with a disk that has part 
> of the data already in place, it will ignore files that are identical on the 
> source and target, update those on the target that are older, and add any 
> from the source that are not on the target at all.
> 
> I don't know of a down-side to *rsync*, but maybe more experienced users 
> will offer more input.

RAID disks don't have a normal partition map:

eben@pc:~$  sudo fdisk -l /dev/sdk
Disk /dev/sdk: 931.5 GiB, 1000204886016 bytes, 1953525168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 4096 bytes / 33553920 bytes
Disklabel type: dos
Disk identifier: 0x466ffdd2

Device     Boot Start        End    Sectors   Size Id Type
/dev/sdk1        2048 1953520000 1953517953 931.5G da Non-FS data

eben@pc:~$ sudo dd if=/dev/sdk bs=512 skip=2048 | file -
/dev/stdin: Linux Software RAID version 1.2 (1) 
UUID=4dfe9043:8416bab7:621093d8:bf7aa8c2 name=pc:0 level=1 disks=2

I can see how this would work if I set up the destination RAID and then 
populate it using rsync.  If I want to duplicate the source RAID's component 
disks, can it resume if interrupted?

-- 
-eben   [log in to unmask]
I went to a wedding once that took place in a Faraday cage. The
ceremony was nice, but the reception was horrible.
                                      -- ReactsWithWords on Reddit

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