Alex Barclay wrote:
Apologies if this has been addressed, but looking at some of the sun
blogs and google searches I have not been able to find an answer.
Does ZFS support on write automatic snapshots?
For example, according to defined policy, every time a file is written
a snapshot is created with the diff stored. I can see this being
useful in high security environments and companies that have extreme
regulatory requirements.
I don't think you really want every write, do you ?
Do you really want a snapshot taken very time some application does this:
buf_size = 1 byte.
while (some_condition)
write(fd, buf, buf_size);
What if you have 2 such apps or 10 or 100 ?
Those snapshots wouldn't really be that useful plus it would be very
difficult to know which of them are actually useful - if any. What if
the app is making the disk run at full speed 1 byte at time, thats a lot
of snapshots in a second!
I claim to be a security person and I don't see how that amount of
snapshots is actually good from a security view point. If you really do
want to know about all the writes we can already do that using Solaris
BSM Audit. I believe this is actually better info than taking snapshots
since the audit trail will tell you exactly who did what to what where
they came from and down to a nanosecond (IIRC) when it happened.
Now if what you really mean is snapshot on file closure I think you
might well be on to something useful. Whats more NTFS has some cool
stuff in this area for consolidating identical files. The hooks that
would need to be put into ZFS to do snapshot on file close could be used
for other things like single instance storage (though isn't that the
opposite of ditto blocks on user data hmn whats the opposite of ditto :-)).
> If not, would there be a way besides scripts/programs to emulate this
feature?
Why not scripts and programs how else would we do it ?
You could do this with a very simple dtrace script that uses system() to
do the zfs snapshot.
You can also use dtrace to simulate the every single write case and see
for yourself the massive explosion of snapshots that would occur as a
result.
--
Darren J Moffat
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