From mboxrd@z Thu Jan 1 00:00:00 1970 From: Edward Shishkin Subject: Re: External journals and NVRAM devices Date: Fri, 01 Nov 2002 17:30:18 +0300 Sender: edward Message-ID: <3DC28FFA.462FF30F@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 List-Id: Content-Type: text/plain; charset="us-ascii" To: Jeremy Howard Cc: Andreas Dilger , 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. Yes. And the experience said that external logging brings a bit better effect for this journal mode then for other ones. > >Is there a command to show the current journal size? #debugreiserfs main_device > > Does the size vary over time? We need to ensure we buy a card with > > enough memory so this is important information for us. The journal size remains the same unless you specify another one by reiserfstune utility. Thanks, Edward. > > > > 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/