[DRBD-user] Fwd: Re: Secondary Performance

Adam Goryachev mailinglists at websitemanagers.com.au
Mon Dec 24 08:07:33 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 24/12/12 12:03, Prater, James K. wrote:
> Hello Adam,
> You issue is that your secondary peer is running 8Mbyte behind and you could not make it primary without dumping the original primary.   

Right, but it's only for a couple of seconds.... ie, it falls behind for
a maximum period of 20seconds, (usually 3 - 5 seconds) about 20 times
per day. So what I want to know, is how can I "tune" DRBD to buffer an
additional 8M of data instead of falling behind?

ie, I just need an extra 8M (ok, probably 16M would do it), of write
cache on the secondary between DRBD and the drives.

Sure, ultimately, buying another 5 x SSD's would resolve the issue, but
that just isn't likely to happen any time soon...

On 24/12/12 17:49, Christof.r wrote:
> In our production environment this works out as expected and using the cluster this way around (SSD as primary) delivers around 5-10x the performance as vice versa. We did test this with loading mdir mailboxes with 20k+ messages in a webmail interface that fetches ALL the messages from the server and then sorts in in the frontend afterwards.
> The loading time of such boxes, while SSD is primary, are by magnitudes faster....i.e. 3-4 seconds vs 20-30 (of course while system was in production and thousands of users online)

Yep, I want the primary to provide better performance (because of the
reads) than the secondary. This shouldn't be a problem, just my
secondary is a bit too slow to keep up.... Potentially, upgrading to 6 x
2TB drives in RAID10 would resolve the issue, I can do that with
existing hardware, but then I'm wasting 4TB instead of only 2TB, and I
lose other options with the extra drives (like setting up a 3rd DRBD
server to backup the secondary in a remote location, and just letting it
get out of sync every day, and resync each night)...

Thanks for your advise, I do appreciate it.


Adam Goryachev
Website Managers

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