Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On Thu, May 07, 2009 at 08:13:55PM +0000, Holger Kiehl wrote: > > local: 160 MB/s > > drbd disconnected: 70 MB/s > > AL-transaction latency appears to be: 32142 micro seconds > > you may want to verify this using e.g. > > dd if=/dev/zero of=ll_dev bs=512 count=1000 oflag=direct > > > > there. now, how long does a synchonous single sector write take on you > > lower level device? > > > dd if=/dev/zero of=/dev/md4 bs=512 count=1000 oflag=direct > 1000+0 records in > 1000+0 records out > 512000 bytes (512 kB) copied, 3.38987 s, 151 kB/s right. though, your meta data is "internal", it is at the very end of the device, so all the disks in the md4 raid have to seek to the very end, possibly adjusting rotation speed, do that single sector write, then seek back (again possibly adjusting rotational speed), then write the next 4MB, seek back to the end, do the next transaction, seek to the front again. just for the fun of it, and to rule it out as possible cause, as an experiment, you could place DRBD meta data on a ram disk... -- : Lars Ellenberg : LINBIT HA-Solutions GmbH : DRBD®/HA support and consulting http://www.linbit.com DRBD® and LINBIT® are registered trademarks of LINBIT, Austria. __ please don't Cc me, but send to list -- I'm subscribed