Re: Snapshot performances

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

> How is an internal snapshot defined?
I'm not completely sure. Ask hannken@.

> The term seems to only exist in dump(8).
And fsck_ffs(8).

> Is it a snapshot for which the backing store is on the same disk 
> the snapshot is done?
I suppose. hannken@ should know.

My experience is that I regularily take external snapshots (using fssconfig(8)) 
while doing TSM backups, and this works fine even for multi-TB filesystems. 
However, taking an internal snapshot (fsck -X) on that filesystem starved the 
machine, eventually paniced it (some WAPBL resource exhaustion) and the log 
replay on reboot took something like half an hour. On much smaller filesystems, 
fsck -X works fine.