[DRBD-user] Secondary Performance

Adam Goryachev mailinglists at websitemanagers.com.au
Fri Dec 21 14:04:38 CET 2012

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

On 20/12/12 19:56, Felix Frank wrote:
> On 12/20/2012 08:31 AM, Adam Goryachev wrote:
>> The primary has 5 x 480G Intel SSD drives in a RAID5 configuration
>> The secondary has 4 x 2TB WD RE4 drives in a RAID10 configuration
> Huh. SSD RAID vs. rotaries? That's about as far apart as you can set
> primary and secondary performance-wise. Have you considered switching
> their roles?

Ummm, no, I need the primary to be fast enough for the work-load...

> If I understand this correctly, you're looking for a way to keep your
> maximum performance and trade in the stability of your replication. Are
> you sure the gain is wort the risk (and pain)? Is your iSCSI maxing out
> the I/O on that SSD RAID?

No, the I/O on the SSD is not significant... at least, I don't think it
I thought that since the secondary is a write only mirror, it doesn't
have as much seek overhead because it never has to seek for a read. ie,
if 40% of all disk I/O is a read request, then the secondary has 40%
less load compared to the primary. I hoped that avoiding RAID5 (using
RAID10) on the secondary would allow it to be "good enough".

>> In general, most of those are small amounts of data over small amounts
>> of time, so it would be nice to add a little more buffering 'somewhere'
>> so that instead of getting out of sync, the secondary just has more data
>> un-written to disk in a buffer somewhere.
>> Any suggestions or advice would be greatly appreciated.
> DRBD Proxy springs to mind, even though that's not a free option
> (monetarily speaking).

Thanks, I am aware of that option, and have already proposed that as a
solution, but spending that kind of money is not an option at the
moment. I found performance improved after tuning some of the options in
drbd, and was either looking for other parameters to tune (or test/etc)
to find the bottleneck or solve the bottleneck (at least a little).
However, I didn't find a specific formula for setting those options, and
I don't think its a great option to tweak options and just hope for the

I think I've mentioned before the following options that I am currently
		max-buffers 16000;
		max-epoch-size 16000;
		unplug-watermark 8192;
		sndbuf-size 512k;
		on-congestion pull-ahead;


Adam Goryachev
Website Managers

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