Re: [zfs-discuss] problems with l2arc in 2009.06
correct ratio of arc to l2arc? from http://blogs.sun.com/brendan/entry/l2arc_screenshots It costs some DRAM to reference the L2ARC, at a rate proportional to record size. For example, it currently takes about 15 Gbytes of DRAM to reference 600 Gbytes of L2ARC - at an 8 Kbyte ZFS record size. If you use a 16 Kbyte record size, that cost would be halve - 7.5 Gbytes. This means you shouldn't, for example, configure a system with only 8 Gbytes of DRAM, 600 Gbytes of L2ARC, and an 8 Kbyte record size - if you did, the L2ARC would never fully populate. ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] problems with l2arc in 2009.06
correct ratio of arc to l2arc? from http://blogs.sun.com/brendan/entry/l2arc_screenshots Thanks Rob. Hmm...that ratio isn't awesome. ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] problems with l2arc in 2009.06
Ethan Erchinger wrote: correct ratio of arc to l2arc? from http://blogs.sun.com/brendan/entry/l2arc_screenshots Thanks Rob. Hmm...that ratio isn't awesome. TANSTAAFL A good SWAG is about 200 bytes for L2ARC directory in the ARC for each record in the L2ARC. So if your recordsize is 512 bytes (pathologically worst case), you'll need 200/512 * size of L2ARC for a minimum ARC size, so ARC needs to be about 40% of the size of L2ARC. For 8 kByte recordsize it will be about 200/8192 or 2.5%. Neel liked using 16kByte recordsize for InnoDB, so figure about about 1.2%. In this case, if you have about 150 GBytes of L2ARC disk, and are using 8 kByte recordsize, you'll need at least 3.75 GBytes for the ARC, instead of 2 GBytes. Since this space competes with the regular ARC caches, you'll want even more headroom, so maybe 5 GBytes would be a reasonable minimum ARC cap? -- richard ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] problems with l2arc in 2009.06
This is a mysql database server, so if you are wondering about the smallish arc size, it's being artificially limited by set zfs:zfs_arc_max = 0x8000 in /etc/system, so that the majority of ram can be allocated to InnoDb. I was told offline that it's likely because my arc size has been limited to a point that it cannot utilize l2arc correctly. Can anyone tell me the correct ratio of arc to l2arc? Thanks again, Ethan ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
