On Jun 14, 2010, at 6:35 PM, Erik Trimble wrote: > On 6/14/2010 12:10 PM, Neil Perrin wrote: >> On 06/14/10 12:29, Bob Friesenhahn wrote: >>> On Mon, 14 Jun 2010, Roy Sigurd Karlsbakk wrote: >>> >>>>> It is good to keep in mind that only small writes go to the dedicated >>>>> slog. Large writes to to main store. A succession of that many small >>>>> writes (to fill RAM/2) is highly unlikely. Also, that the zil is not >>>>> read back unless the system is improperly shut down. >>>> >>>> I thought all sync writes, meaning everything NFS and iSCSI, went into the >>>> slog - IIRC the docs says so. >>> >>> Check a month or two back in the archives for a post by Matt Ahrens. It >>> seems that larger writes (>32k?) are written directly to main store. This >>> is probably a change from the original zfs design. >>> >>> Bob >> >> If there's a slog then the data, regardless of size, gets written to the >> slog. >> >> If there's no slog and if the data size is greater than >> zfs_immediate_write_sz/zvol_immediate_write_sz >> (both default to 32K) then the data is written as a block into the pool and >> the block pointer >> written into the log record. This is the WR_INDIRECT write type. >> >> So Matt and Roy are both correct. >> >> But wait, there's more complexity!: >> >> If logbias=throughput is set we always use WR_INDIRECT. >> >> If we just wrote more than 1MB for a single zil commit and there's more than >> 2MB waiting >> then we start using the main pool. >> >> Clear as mud? This is likely to change again... >> >> Neil. >> > > How do I monitor the amount of live (i.e. non-committed) data in the slog? > I'd like to spend some time with my setup, seeing exactly how much I tend to > use.
zilstat http://www.richardelling.com/Home/scripts-and-programs-1/zilstat > I'd suspect that very few use cases call for more than a couple (2-4) GB of > slog... I'd suspect few real cases need more than 1GB. -- richard -- Richard Elling rich...@nexenta.com +1-760-896-4422 ZFS and NexentaStor training, Rotterdam, July 13-15, 2010 http://nexenta-rotterdam.eventbrite.com/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
