I was playing with a Gigabyte i-RAM card and found out it works great
to improve overall performance when there are a lot of writes of small
files over NFS to such a ZFS pool.
However, I noted a frequent situation in periods of long writes over
NFS of small files. Here's a snippet of iostat during that period.
sd15/sd16 are two iscsi targets, and sd17 is the iRAM card (2GB)
extended device statistics
device r/s w/s kr/s kw/s wait actv svc_t %w %b
sd15 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd16 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd17 0.0 0.0 0.0 0.0 3.0 1.0 0.0 100 100
extended device statistics
device r/s w/s kr/s kw/s wait actv svc_t %w %b
sd15 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd16 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd17 0.0 0.0 0.0 0.0 3.0 1.0 0.0 100 100
extended device statistics
device r/s w/s kr/s kw/s wait actv svc_t %w %b
sd15 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd16 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd17 0.0 0.0 0.0 0.0 3.0 1.0 0.0 100 100
extended device statistics
device r/s w/s kr/s kw/s wait actv svc_t %w %b
sd15 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd16 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd17 0.0 0.0 0.0 0.0 3.0 1.0 0.0 100 100
extended device statistics
device r/s w/s kr/s kw/s wait actv svc_t %w %b
sd15 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd16 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd17 0.0 0.0 0.0 0.0 3.0 1.0 0.0 100 100
extended device statistics
device r/s w/s kr/s kw/s wait actv svc_t %w %b
sd15 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd16 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd17 0.0 0.0 0.0 0.0 3.0 1.0 0.0 100 100
extended device statistics
device r/s w/s kr/s kw/s wait actv svc_t %w %b
sd15 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd16 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd17 0.0 0.0 0.0 0.0 3.0 1.0 0.0 100 100
extended device statistics
device r/s w/s kr/s kw/s wait actv svc_t %w %b
sd15 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd16 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd17 0.0 0.0 0.0 0.0 3.0 1.0 0.0 100 100
extended device statistics
device r/s w/s kr/s kw/s wait actv svc_t %w %b
sd15 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd16 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
sd17 0.0 0.0 0.0 0.0 3.0 1.0 0.0 100 100
During this time no operations can occur. I've attached the iRAM disk
via a 3124 card. I've never seen a svc_t time of 0, and full wait and
busy disk. Any clue what this might mean?
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