Even if I set zfs_write_limit_override to 8053063680 I am unable to
achieve the massive writes that Solaris 10 (141415-03) sends to my
drive array by default.
When I read the blog entry at
http://blogs.sun.com/roch/entry/the_new_zfs_write_throttle, I see this
statement:
"The new code keeps track of the amount of data accepted in a TXG and
the time it takes to sync. It dynamically adjusts that amount so that
each TXG sync takes about 5 seconds (txg_time variable). It also
clamps the limit to no more than 1/8th of physical memory."
On my system I see that the "about 5 seconds" rule is being followed,
but see no sign of clamping the limit to no more than 1/8th of
physical memory. There is no sign of clamping at all. The writen
data is captured and does take about 5 seconds to write (good
estimate).
On my system with 20GB of RAM, and ARC memory limit set to 10GB
(zfs:zfs_arc_max = 0x280000000), the maximum zfs_write_limit_override
value I can set is on the order of 8053063680, yet this results in a
much smaller amount of data being written per write cycle than the
Solaris 10 default operation. The default operation is 24 seconds of
no write activity followed by 5 seconds of write.
On my system, 1/8 of memory would be 2.5GB. If I set the
zfs_write_limit_override value to 2684354560 then it seems that about
1.2 seconds of data is captured for write. In this case I see 5
seconds of no write followed by maybe a second of write.
This causes me to believe that the algorithm is not implemented as
described in Solaris 10.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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