[DRBD-user] Reducing loadavg / iowait? a few more questions

Lars Ellenberg Lars.Ellenberg at linbit.com
Wed Aug 3 08:06:44 CEST 2005

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

> > Q2: Can one change to protocol B on-the-fly using 'drbdadm adjust'?
> No clue, maybe the linbit people (Lars?) know?

not while connected (changing protocol does a reconnect,
and protocol mismatch causes connection abort).
so you'd have to disconnect both nodes,
then adjust the protocol on both nodes
(which should imlicitly reconnect).

 on R # vi drbd.conf
 on R # scp drbd.conf Q:

 on R # drbdadm disconnect
 on Q # drbdadm disconnect

 on R # drbdadm adjust
 on Q # drbdadm adjust

(no need to stop services, though)

> > drbd hot area) Currently we use 521 al-extents for a 1.4 TB device. How
> > much difference does it make when we increase this number? (nr of writes
> > vs. size of al-extents) And also can this be changed on-the-fly?

while the system is under load, try:
  watch -n1 cat /proc/drbd
and keep looking at this "al:###" number
if it changes too frequently, it may help to increase the al size.
if it does not change at all for several seconds/minutes while the dw
and ns numbers are still moving, then it is big enough, and you may even
consider to reduce it (less resync time in case of a Primary crash).

btw, if you get EBUSY during al-size adjustment, just do a
"drbdsetup /dev/drbdX syncer" (no further arguments) several
times until it hits a window where it is not busy... should work.

: Lars Ellenberg                                  Tel +43-1-8178292-0  :
: LINBIT Information Technologies GmbH            Fax +43-1-8178292-82 :
: Schoenbrunner Str. 244, A-1120 Vienna/Europe   http://www.linbit.com :
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