Re: Problem identified: WAPL/RAIDframe performance problems

["J. Hannken-Illjes" <hannken%eis.cs.tu-bs.de@localhost>]

On Nov 28, 2012, at 6:02 PM, Greg Troxel <gdt%ir.bbn.com@localhost> wrote:

> 
> Edgar Fuß <ef%math.uni-bonn.de@localhost> writes:
> 
>>> I seem to be facing two problems:
>>> 
>>> 1. A certain svn update command is ridicously slow on my to-be file server.
>>> 2. During the svn update, the machine partially locks up and fails to 
>>> respond 
>>>   to NFS requests.
>> Thanks to very kind help by hannken@, I now at least know what the problem 
>> is.
>> 
>> Short form: WAPBL is currently completely unusable on RAIDframe (I always 
>> suspected something like that), at least on non-Level 0 sets.
>> 
>> The problem turned out to be wapbl_flush() writing non-fsbsize chunks on non-
>> fsbsize boundaries. So RAIDframe is nearly sure to RMW.
>> That makes the log being written to disc at about 1MB/s with the write lock 
>> on the log being held. So everything else on that fs tstiles on the log's 
>> read lock.
> 
> Do you see this on RAID-1 too?
> 
> I wonder if it's possible (easily) to make the log only use fsbize
> boundaries, (maybe forcing it to be bigger as a side effect.)


Sure -- add fsbsize sized buffer to struct wapbl and teach wapbl_write()
to collect data until the buffers start or end touches a fsbsize boundary.

As long as the writes don't cross the logs end they already come ordered.

--
J. Hannken-Illjes - hannken%eis.cs.tu-bs.de@localhost - TU Braunschweig 
(Germany)