[DRBD-user] DRBD with iSCSI vs NFS issue

Gerald Brandt gbr at majentis.com
Sat Nov 30 18:00:20 CET 2013

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


I've been running DRBD on my servers for quite some time on some servers at a clients (a little over a year with this client, I believe).  I've been exporting drbd0 as iSCSI for the entire time.  Write tests over GigE (1B block size, sequential write) gives me an everage of 118MB/s.  Very good.

Last week, I switched drbd0 from iSCSI to NFSv3 exports.  

Performing the same test (I use XenServer Performance VM tool), I get very strange behaviour.  atop shows an average write speed of ~35 MB/s.  The Perf Tool shows 117-118 MB/s, with drops down to 0MB/s.  There are a lot of drops, and the average via the tool equals what atop shows.

If I remove the secondary, performance via NFS jumps and stays at 117-118 MB/s.

The underlying DRBD config has not changed at all.

Why am I seeing the difference between iSCSI exports on drbd0 vs NFS exporst on drbd0, only when the secondary is attached?


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