On 10/04/12 15:59, Edward Ned Harvey (opensolarisisdeadlongliveopensolaris)
wrote:
From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
boun...@opensolaris.org] On Behalf Of Neil Perrin
The ZIL code chains blocks together and these are allocated round robin
among slogs or
if they don't exist then the main pool devices.
So, if somebody is doing sync writes as fast as possible, would they gain more
bandwidth by adding multiple slog devices?
In general - yes, but it really depends. Multiple synchronous writes of any size
across multiple file systems will fan out across the log devices. That is
because there is a separate independent log chain for each file system.
Also large synchronous writes (eg 1MB) within a specific file system will be
spread out.
The ZIL code will try to allocate a block to hold all the records it needs to
commit up to the largest block size - which currently for you should be 128KB.
Anything larger will allocate a new block - on a different device if there are
multiple devices.
However, lots of small synchronous writes to the same file system might not
use more than one 128K block and benefit from multiple slog devices.
Neil.
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