[rrd-users] Inquiring on how to ease disk io (linux).

Raimund Berger raimund.berger at gmail.com
Wed Jun 25 20:27:04 CEST 2008

"Bernard Li" <bernard at vanhpc.org> writes:

> I am not too familiar with stack mounting -- how is your solution
> different from putting all the rrds in tmpfs?

Well, with tmpfs you need to populate it with RRD's on startup, and
write back to disk at specified intervals or at least on shutdown.

Stacking a tmpfs - which I do also use - over the disk takes care at
least of the first part by implementing a simple copy on write. So you
don't have to take care of tmpfs population anymore.

Unfortunately, nobody yet seems to have foreseen use cases like ours.
So the second part, syncinc back, apparently isn't yet supported.

Typically, stacking is used to mount tmpfs over ro media in
installation/diskless/(quasi)embedded situations to simulate writable
mounts, so historically they came from a different angle.

I haven't yet fully investigated the current state of things though,
so there might even be a solution out there right now resp.
corresponding work being in progress.

> I was thinking it would be ideal to put all the rrds in a hybrid
> tmpfs/regular fs where data is written to tmps and periodically synced
> to the regular fs.  Most folks who put rrds in tmpfs have some cronjob
> to do this incase of server crash, but ideally this could be dealt
> with by some fs hooks.  Maybe using inotify or something like that.
> You might also be interested in this thread over at rrd-developers:
> http://www.mail-archive.com/rrd-developers@lists.oetiker.ch/msg02284.html

Cool, more stuff to read. Thanks a bunch.

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