[DRBD-user] DRBD with iSCSI vs NFS issue

Mark Coetser mark at tux-edo.co.za
Tue Dec 3 14:19:27 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.

On 03/12/2013 15:06, Gerald Brandt wrote:
> Anybody have an idea whats happened (see below)?  The iSCSI and NFS load are both KVM images (iSCSI is LVM based).
> Gerald
> ----- 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


I have a similar issue (look for my recent post), except my issue causes 
load on my nfs clients to climb under lots or read/writes, I have 
lowered the impact now by adjusting the nfs mount options. According to 
the research I have done the slower speeds of nfs are just the nature of 
the nfs server due to it being a "shared" file system where as iscsi is 
dedicated to a single hosts read/writes.

Thank you,

Mark Adrian Coetser

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