[DRBD-user] DRBD with iSCSI vs NFS issue

Gerald Brandt gbr at majentis.com
Tue Dec 3 14:06:55 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.

Anybody have an idea whats happened (see below)?  The iSCSI and NFS load are both KVM images (iSCSI is LVM based).


----- Original Message -----
> From: "Gerald Brandt" <gbr at majentis.com>
> To: drbd-user at lists.linbit.com
> Sent: Saturday, November 30, 2013 11:00:20 AM
> Subject: [DRBD-user] DRBD with iSCSI vs NFS issue
> Hi,
> 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?
> Gerald
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