> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of Chris Twa > > My plan now is to buy the ssd's and do extensive testing. I want to > focus my performance efforts on two zpools (7x146GB 15K U320 + 7x73GB > 10k U320). I'd really like two ssd's for L2ARC (one ssd per zpool) and > then slice the other two ssd's and then mirror the slices for SLOG (one > mirrored slice per zpool). I'm worried that the ZILs won't be > significantly faster than writing to disk. But I guess that's what > testing is for. If the ZIL in this arrangement isn't beneficial then I > can have four disks for L2ARC instead of two (or my wife and I get > ssd's for our laptops).
Remember that ZIL is only for sync writes. So if you're not doing sync writes, there is no benefit of a dedicated log device. Also, for a lot of purposes, disabling ZIL is actually viable. It's zero cost which guarantees absolute optimal performance on spindle disks. Nothing is faster. To quantify the risk, here's what you need to know: In the event of an ungraceful crash, up to 30sec of async writes are lost. Period. But as long as you have not disabled ZIL, then all the sync writes were not lost. If you have ZIL disabled, then sync=async. Up to 30sec of all writes are lost. Period. But there is no corruption or data written out-of-order. The end result is as-if you halted the server suddenly, flushed all the buffers to disk, and then powered off. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
