On Wed, May 14, 2008 at 12:15 AM, Jordan Mendler <jmendler@xxxxxxxx> wrote: > Hi all, > > I am in the process of implementing write-behind and had some questions. > > 1) I've been told aggregate-size should be between 0-4MB. What is the > down-side to making it large? In our case (a backup server) I would think > the bigger the better since we are doing lots of consecutive/parallel > rsyncs > of a combination of tons of small files and some very large files. The only > down-side I could see is that small transfers are not distributed as evenly > since large writes will be done to only 1 brick instead of half of the > write > to each brick. Perhaps someone can clarify. > Currently we have a upper limit in our protocol translator to transfer only 4MB of data at the max in one request/reply packet. Hence if you use write-behind on client side (as in most of the cases), it will fail to send the bigger packet. > > 2) What does flush-behind do? What is the advantage of having it on and > what > is the advantage of it off. > this option is given for increasing the performance of handling lot of small files where, the close()/flush() can be pushed to back-ground, hence client can process the next request. Its ''off'' by default. > > 3) write-behind on the client aggregates small writes into larger ones. Is > there any purpose to doing it on the server side? If so, how is this > helpful? > Yes, generally, it helps if the writes are coming in a very small chunk. It helps to reduce the diskhead seek() time. > > 4) should write-behind be done on a brick-by-brick basis on the client, or > is it fine to do it after the unify? (seems like it would be fine since > this > would consolidate small writes before sending it to the scheduler). > Yes, the behavior will be same where ever you put it. But its advised to do it after unify as it reduces the complexity of the spec file. > Hardware wise we currently have 2 16x1TB Hardware RAID6 servers (each is > 8core, 8gb of RAM). Each acts as both a server and a unify client. > Underlying filesystem is currently XFS on Linux, ~13TB each. Interconnect > is > GigE and eventually we will have more external clients, though for now we > are just using the servers as clients. My current client config is below. > Any other suggestions are also appreciated. > Spec file looks good. Regards, -- Amar Tumballi Gluster/GlusterFS Hacker [bulde on #gluster/irc.gnu.org] http://www.zresearch.com - Commoditizing Super Storage!
