Re: [BUG] non-metadata arrays cannot use more than 27 component devices

[Phil Turmel <philip@turmel.org>]

On 02/25/2017 03:05 PM, Anthony Youngman wrote:

> Although I would have thought build mode was superb for doing
> backups without needing to stop using the system ... I haven't seen
> any documentation about things like breaking raid to do backups and
> all that sort of thing.
> 
> I need to investigate it, but I'd like to know how to suspend a
> mirror, back it up, and then resume. The databases I work with have
> an option that suspends all new writes, but flushes all current
> transactions to disk so the disk is consistent for backing up. So if
> you do that and back up the database you know your backup is
> consistent.
> 
> This is all a rather important usage of raid, actually, imho. It
> seems so obvious - create a temporary mirror, wait for the sync to
> complete, suspend i/o to get the disk consistent, then you can break
> the mirror and carry on. Terabytes :-) of data safely backed up in
> the space of seconds.

No. Don't go there.  There's already a technology out there that does
this correctly, called LVM snapshots.  And they let you resume normal
operations after a very brief hesitation, and the snapshot holds the
static image while you copy it off.

Phil