Tomas Ögren wrote: > 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. >
Are you sure this is a prefetch, or is it just the recordsize? The checksum is based on the record, so to validate the checksum the entire record must be read. If you have a fixed record record sized workload where the size < 128 kBytes, then you might adjust the recordsize parameter. -- richard > 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 > _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
