On 16 October, 2008 - Darren J Moffat sent me these 1,7K bytes: > Tomas Ögren wrote: > > On 15 October, 2008 - Richard Elling sent me these 4,3K bytes: > > > >> Tomas Ögren wrote: > >>> Hello. > >>> > >>> Executive summary: I want arc_data_limit (like arc_meta_limit, but for > >>> data) and set it to 0.5G or so. Is there any way to "simulate" it? > >>> > >> We describe how to limit the size of the ARC cache in the Evil Tuning > >> Guide. > >> http://www.solarisinternals.com/wiki/index.php/ZFS_Evil_Tuning_Guide > > > > Will that limit the _data_ portion only, or the metadata as well? > > Recent builds of OpenSolaris have the ability to control on a per > dataset basis what is put into the ARC and L2ARC using the > primrarycache and secondarycache dataset properties: > > primarycache=all | none | metadata > > Controls what is cached in the primary cache (ARC). If > this property is set to "all", then both user data and > metadata is cached. If this property is set to "none", > then neither user data nor metadata is cached. If this > property is set to "metadata", then only metadata is > cached. The default value is "all". > > secondarycache=all | none | metadata > > Controls what is cached in the secondary cache (L2ARC). > If this property is set to "all", then both user data > and metadata is cached. If this property is set to > "none", then neither user data nor metadata is cached. > If this property is set to "metadata", then only meta- > data is cached. The default value is "all".
Yeah, the problem is (like I wrote in the first post), if I set primarycache=metadata, then ZFS prefetch will go into "horribly inefficient mode" where it will do lots of prefetching, but the prefetched data will be discarded immediately. 128k prefetch for a 32k read will throw away the other 96k immediately. Followed by another 128k prefetch for the next 32k read, throwing away the other 96k. So ZFS needs to have _some_ data cache, but I want to limit it for "short term data" only.. Setting data cache limit to 512M or something should work fine, but I want to leave the rest to metadata as that's the place where it can help the most. Unless I can do some trickery with a ram disk and put that as secondarycache with data cache as well.. /Tomas -- Tomas Ögren, [EMAIL PROTECTED], http://www.acc.umu.se/~stric/ |- Student at Computing Science, University of Umeå `- Sysadmin at {cs,acc}.umu.se _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
