On Dec 20, 2009, at 12:25 PM, Tristan Ball wrote:
I've got an opensolaris snv_118 machine that does nothing except
serve up NFS and ISCSI.
The machine has 8G of ram, and I've got an 80G SSD as L2ARC.
The ARC on this machine is currently sitting at around 2G, the
kernel is using around 5G, and I've got about 1G free.
Yes, the ARC max is set by default to 3/4 of memory or memory - 1GB,
whichever
is greater.
http://src.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/fs/zfs/arc.c#3426
I've pulled this from a combination of arc_summary.pl, and 'echo
"::memstat" | mdb -k'
IMHO, it is easier to look at the c_max in kstat.
kstat -n arcstats -s c_max
It's my understanding that the kernel will use a certain amount of
ram for managing the L2Arc, and that how much is needed is
dependent on the size of the L2Arc and the recordsize of the zfs
filesystems
Yes.
I have some questions that I'm hoping the group can answer...
Given that I don't believe there is any other memory pressure on the
system, why isn't the ARC using that last 1G of ram?
Simon says, "don't do that" ? ;-)
Is there some way to see how much ram is used for L2Arc management?
Is that what the l2_hdr_size kstat measures?
Is it possible to see it via 'echo "::kmastat" | mdb -k '?
I don't think so.
OK, so why are you interested in tracking this? Capacity planning?
From what I can tell so far, DDT is a much more difficult beast to
measure
and has a more direct impact on performance :-(
-- richard
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