On 11/20/08 12:52, Danilo Poccia wrote: > Hi, > > I was wondering is there is a performance gain for an OLTP-like workload > in putting the ZFS Intent Log (ZIL) on "traditional" HDDs. >
It's probably always best to benchmark it yourself, but my experience has shown that it's better to only have a separate log when the log devices are faster. Without a separate log (slog) the log is allocated dynamically from the pool and at a location where current allocations are happening for transaction groups. So there is little head movement needed to write the log. There may be a problem when the pool is very full and fragmented as log block allocation will be all over the place and seek latency will be high. However, this is a problem for the whole pool. Also, the log is spread across the pool devices so the more devices in the pool the faster the intent log can be written when the load is heavy. Hope that helps: Neil. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
