Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
Holger Kiehl wrote: > On Thu, 7 May 2009, Lars Ellenberg wrote: > >> 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... >> > I will try this tommorrow and report what I get. Is there some documentation > on how to do this? How do I get the size of DRBD meta data? The formula for calculating the meta-data can be found at the link below, I would assume just use external meta-data, which can also be found in the guide below :) http://www.drbd.org/users-guide/ch-internals.html#s-meta-data-size > > Many thanks for all the help! > > Holger > _______________________________________________ > drbd-user mailing list > drbd-user at lists.linbit.com > http://lists.linbit.com/mailman/listinfo/drbd-user