[DRBD-user] DRBD - Slow Performance

Kavan Smith kavan at linbit.com
Mon Feb 15 23:57:25 CET 2010

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

Hi Dan,

Without getting too deep into your stack....can you test this with a
local (LAN) based DRBD resource vs. a remote one?

Even with 28ms of latency, there could be something in your network
causing some bottlenecks stopping DRBD from doing it's job properly.

I've seen high-bandwidth low-latency links act similarly due to an
unseen network policy (not DRBD's fault, simply put...you can't put a
man on the moon without the proper fuel...no fuel no fly).

If I understand correctly what your layout is...it would be wise to
segment your servers from your network to troubleshoot.  If DRBD works
great in a LAN environment (cross connect) cable....then it is not your
server, it is your network.

Vice versa....if it works horribly with a cross connect as well...then
you have something going on inside your server...software or hardware.

Hope this helps.


Dan Lavu wrote:
> Digi,
> I posted most everything on the initial email, but to recap, I'm pretty
> sure it's a disk issue. 
> When copying a large file to the raid, using SFTP I see IO read and
> write times of 30-35MB/s and I see transfer rates of 20MB/s. Keep in
> mind I'm syncing between two datacenters, Texas to Illinois. 
> When it's syncing, iostat shows read write times of 2MB/s. I even
> created a ramdisk for an external metadisk and I saw no improvement. 
> If my raid can easily write at 30MB/s why is the DRBD sync capped at
> 2MB/s? This is a RAID 5, with two logical volumes. 
> Thanks,
> Dan Lavu 
> -----Original Message-----
> From: Digimer [mailto:linux at alteeve.com] 
> Sent: Monday, February 15, 2010 5:30 PM
> To: Dan Lavu
> Cc: drbd-user at lists.linbit.com
> Subject: Re: [DRBD-user] DRBD - Slow Performance
> Dan Lavu wrote:
>> Digi,
>> Thanks for advance again, but I've already tried this. I'm still
> pegged
>> at 2MB/s. I've exhausted IRC any google searches involving DRBD slow
>> sync. I'm really contemplating rebuilding the machine with a RAID 10
> to
>> enhance performance but I still do not know if this is going to
> resolve
>> the issue, any thoughts about this? Thanks in advance.
>> Best Regards,
>> Dan Lavu
> How is performance on the local disk? Have you checked using something 
> like: fdisk -tT /dev/sda? Also, what performance do you get if you write
> a large file to the array?
> What I am wondering is; Is the performance limitation a DRBD issue, a 
> disk issue or a sync'er issue. What kind of performance do you get 
> sending a file over the DRBD's network interfaces directly (not writing 
> to the DRBD disk)?
> Digi
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: Kavan Smith
: LINBIT | Your Way to High Availability
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