On 24/02/17 20:46, Phil Turmel wrote:
On 02/24/2017 11:40 AM, ian_bruce@xxxxxxx wrote:
On Fri, 24 Feb 2017 10:20:52 -0500 Phil Turmel <philip@xxxxxxxxxx>
wrote:
Considering the existence of --build is strictly to support arrays
that predate MD raid, it seems a bit of a stretch to claim this as
a bug instead of a feature request.
quoting from the mdadm manual page:
Quote all you like, it doesn't change the history. Note that build mode
doesn't support a bunch of other MD raid features either, like all of
the parity raid levels. That it doesn't support v1+ metadata isn't a
surprise, and isn't the only legacy feature that only uses legacy
metadata (built-in kernel auto-assembly gets the most whining, actually).
Anyways, though I can't speak for the maintainers, it seems that build
mode is there to keep the MD maintainers from being yelled at by Linus
for breaking legacy setups. Nothing more.
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.
Cheers,
Wol
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