Snapshot duration, performance and how to avoid I/O lock

[Philippe Pegon]

Ulrich Spörlein wrote:
> Hi,

Hi,

> I have to create regular snapshots of several volumes roughly 1.4TB in 
> size (each). But using mksnap_ffs takes a lot of time (45 minutes) and
> it looks like it could be speed up.
[snip]
> Another thing is blocking other disk I/O while snapshotting. Right now I did
> a ls(1) in the .snap directory, so I understand the filesystem is now suspended.
> The workaround would then be to "dont do that". But what if other snapshots are
> accessed during that time? I want to provide yesterdays snapshot to our users
> while taking the current snapshot and providing access to the newest data at the
> same time.

I had seen that a long time ago (on another controller), and it seems it's
not better today, our post from june 2005 without response at the end :

http://docs.freebsd.org/cgi/getmsg.cgi?fetch=410600+0+archive/2005/freebsd-stable/20050612.freebsd-stable

http://docs.freebsd.org/cgi/getmsg.cgi?fetch=463968+0+archive/2005/freebsd-stable/20050612.freebsd-stable

--
Philippe Pegon