From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hans Reiser Subject: Re: External journals and NVRAM devices Date: Fri, 01 Nov 2002 23:41:55 +0300 Message-ID: <3DC2E713.3000309@namesys.com> References: <3DC21358.5040808@fastmail.fm> <20021101062957.GE554@clusterfs.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: list-help: list-unsubscribe: list-post: Errors-To: flx@namesys.com In-Reply-To: <3DC21358.5040808@fastmail.fm> List-Id: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Andreas Dilger Cc: Jeremy Howard , ReiserFS List Andreas Dilger wrote: >On Nov 01, 2002 16:38 +1100, Jeremy Howard wrote: > > >>I'm looking at buying solid state drives / NVRAM drives for our servers >>to hold an external ReiserFS journal. >> >>We are using 2.4.20pre11, and Chris Mason's data logging patches. >> >>I'm looking for any tips on how large the journal is when using >>data=journal, and whether the external log patches are stable and work OK >>in data=journal mode. Is there a command to show the current journal >>size? Does the size vary over time? We need to ensure we buy a card with >>enough memory so this is important information for us. >> >>Is anyone currently using NVRAM for the journal? If so, how do you find >>the performance of this configuration? >> >> > >When people were testing this with ext3 external journals, they just >used a RAMDISK for getting the performance measurements. Obviously, >(I hope ;-) this is not something you can do in real life, but for >performance measurement it is OK. > >Most people found that the ramdisk (and presumably the NVRAM device too) >didn't perform much, if any, better than having a separate fast disk for >the journal, because you are doing sequential I/O to the journal anyways. >If it is on a separate disk/controller from the filesystem you don't have >any seek or channel contention with the filesystem. Of course, using a >regular disk for the journal is MUCH cheaper than an NVRAM card, so you >probably want to test this out before you go ahead and buy the NVRAM card. > >NVRAM devices are great for disks you are doing a lot of random I/O >on (maybe database indexes or something), because there is zero seek >latency, but for sequential I/O (like the journal) it really isn't >anything special. > >Cheers, Andreas >-- >Andreas Dilger >http://www-mddsp.enel.ucalgary.ca/People/adilger/ >http://sourceforge.net/projects/ext2resize/ > > > > > NVRAM devices are for fsync intensive operations. -- Hans