Can someone confirm the following calculation of SSD size for SLOG / ZIL device is correct?
-- Assumption --
HDD each can write 150MB/s
So a zpool of 4 HDD will write 600MB/s
-- Calculation --
1) The transaction group (txg) size will be 3GB
(600MB/s x 5 sec where txg by default will flush data every 5 sec)
2) The system memory size should kept no more than 24GB
(3GB x 1/8 where txg by default use up to 1/8 system's memory)
3) The SSD should be partitioned to 12GB (leave the rest of the SSD unallocated) for slog / ZIL device
(The maximum size of a log device should be approximately 1/2 the size of physical memory because that is the maximum amount of potential in-play data that can be stored)
Reference from:
http://forums.freenas.org/threads/some-insights-into-slog-zil-with-zfs-on-freenas.13633/
(see Tangent: Dangers of overly large ZFS write cache)
http://docs.oracle.com/cd/E26502_01/html/E29007/gaypw.html#gffyt
(see Creating a ZFS Storage Pool With Log Devices)
Side notes:
http://hardforum.com/showthread.php?t=1551326
(this post suggest the txg size and time can be changed)
http://forums.freenas.org/threads/how-to-partition-zil-ssd-drive-to-underprovision.11824/#post-54426
(this post mention SLOG size should keep small)
http://forums.freenas.org/threads/how-to-add-an-slog.16766/#post-87093
(this post teach you how to partition SSD for the right SLOG size)
http://forums.freenas.org/threads/s...l-with-zfs-on-freenas.13633/page-3#post-83945
(Large RAM, small pool, performance example)
-- Assumption --
HDD each can write 150MB/s
So a zpool of 4 HDD will write 600MB/s
-- Calculation --
1) The transaction group (txg) size will be 3GB
(600MB/s x 5 sec where txg by default will flush data every 5 sec)
2) The system memory size should kept no more than 24GB
(3GB x 1/8 where txg by default use up to 1/8 system's memory)
3) The SSD should be partitioned to 12GB (leave the rest of the SSD unallocated) for slog / ZIL device
(The maximum size of a log device should be approximately 1/2 the size of physical memory because that is the maximum amount of potential in-play data that can be stored)
Reference from:
http://forums.freenas.org/threads/some-insights-into-slog-zil-with-zfs-on-freenas.13633/
(see Tangent: Dangers of overly large ZFS write cache)
http://docs.oracle.com/cd/E26502_01/html/E29007/gaypw.html#gffyt
(see Creating a ZFS Storage Pool With Log Devices)
Side notes:
http://hardforum.com/showthread.php?t=1551326
(this post suggest the txg size and time can be changed)
http://forums.freenas.org/threads/how-to-partition-zil-ssd-drive-to-underprovision.11824/#post-54426
(this post mention SLOG size should keep small)
http://forums.freenas.org/threads/how-to-add-an-slog.16766/#post-87093
(this post teach you how to partition SSD for the right SLOG size)
http://forums.freenas.org/threads/s...l-with-zfs-on-freenas.13633/page-3#post-83945
(Large RAM, small pool, performance example)