[DRBD-user] Write performance again

Sebastian Riemer sebastian.riemer at profitbricks.com
Wed Sep 26 15:49:07 CEST 2012

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

Hi Roland,

I've analysed the DRBD 8.4.1 kernel code some time ago.

DRBD has a dynamic IO request size detection which always starts at 4
KiB. If you've got a connection to the other system, then it negotiates
a higher IO request size (128 KiB because of hashing functions). If you
loose the connection, it's 4 KiB again.

You can use the tool "blktrace" to trace how big the IO requests are. Or
you can look at /sys/block/drbd0/queue/max_sectors_kb.

IMHO this must become settable to the limits from the devices below if
you already know that "max_sectors_kb" is completely equal on both sides.



On 26.09.2012 14:50, Roland Kaeser wrote:
> Only the drbd is very slow. (Single node, just to test write
> perfomance on local block device.

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