[DRBD-user] Mirroring /var

Lars Ellenberg Lars.Ellenberg at linbit.com
Fri Jan 16 18:34:23 CET 2004

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

/ 2004-01-16 12:02:24 -0500
\ Weed:
> 	I was wondering if anyone could think of a logical way for me to mirror
> my whole /var partition.  From what I've read so far, it doesn't seem
> possible. Thanks for any help.

It would help to know WHY you want to do this.
What exactly is in your /var that is needed on the other node
after a shutdown?

you want to mirror:
/var/adm        probably not.

/var/lib        some parts of it
/var/lib/rpm    certainly not.
/var/lib/samba  maybe
/var/lib/mysql  (or similar) maybe
/var/lib/nfs    maybe
/var/lib/drbd   CERTAINLY NOT
/var/log        probably not, maybe parts of it
/var/X11R6      certainly not

/var/cache      maybe parts of it
/var/lock       certainly not
/var/named      maybe
/var/run        certainly not

/var/spool      parts of it?
/var/spool/clientmqueue    ?
/var/spool/lpd          maybe
/var/spool/mail         maybe
/var/spool/uucp         maybe
/var/spool/atjobs       probably not
/var/spool/atspool      probably not
/var/spool/postfix      likely
/var/spool/cron         probably not
/var/spool/cups         likely
/var/tmp                unlikely

I someone of you wants to write a recommendation list for
reference with some more verbose substantiation why (not) to put
a certain LSB directory on DRBD, we are happy to add that to the
documentaion/howto/drbd.org pages!

To have "static" [read: "changing every six month during maintenance"]
data "higly available", a static copy is obviously completely adequat.
And can easily be kept in sync by other means (rsync, scp, whatever).

You only want to have frequently changing application data on drbd.
Mail spool dirs, NFS lock dir, databases, file shares... Maybe
some temporary "session" related data -- think of web applications.

But it is simply not useful to have your binaries, libraries,
static html content, scripts, host-specific data, ..., on DRBD.

To achieve this, the most easy way is probably symlinks.

Set up one drbd, put the data directories on it, and put symlinks
in place where the application expects its data to be.

	Lars Ellenberg

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