Re: [PLUG] Best tool to image a dynamic disk?

brent timothy saner <brent.saner@gmail.com> · Mon, 6 Mar 2017 16:19:52 -0500

On 03/06/2017 04:01 PM, Greg Helledy wrote:
> We have a couple of servers using dynamic disks with GUID partition
> tables.  They hold mdadm volumes (linux software RAID).
> 
> A co-worker suggested making an image of the drives, to have something
> to start with in case of a major failure.  We went to use a tool he's
> relied on called Paragon, which boots off a DVD into a Windows OS to
> perform the operation.  But it cannot do dynamic disks.
> 
> Does anyone have a recommendation for the best tool to use to make
> images of the dynamic disks on our servers?
> 
> Thanks,

Welp, you're in a bit of a sticky wicket and you might need to clarify.

"Dynamic disks" are a Windows term for proprietary MSFT tech.

mdadm disks/members- the actual disks- can be done with DD no problem.
DD is block-level; it doesn't care what the heck is on the drives.
Paragon and various other software generally try to do some trickery
like shrinking the image by removing unused space- to do that, it needs
to parse the filesystems. Windows doesn't know what the heck to do with
ext2/3/4, btrfs, etc. (let alone an mdadm-managed level of abstraction,
which is between the block level and the filesystem level.)

Long story short, depends on the RAID configuration. If it's RAID1, no
problem- just image one of the members and you're good to go. You can
rebuild the RAID1 from just one member disk and a blank disk. If it's
RAID0 or any other type (RAID5, RAID10, RAID50, etc.) you're going to
need a huge destination, because then you need to dd the entire MD
device (and ideally do it while it isn't mounted).

But, of course, instead of this route, I'd instead recommend a baremetal
backup. If you want something commercial, R1Soft has a pretty good one-
but if opensource is more your speed, my podcast dives pretty deep on
this. (It's totally not safe for work, by the way. Listen when you get
home unless your workplace is really lax.)

The topic of backups is one of our primary talking points in this episode:
https://sysadministrivia.com/episodes/S0E6

Also useful: archiving! (Which is different from, but related to, backups):
https://sysadministrivia.com/episodes/S0E17

Hope this helps.