I would expect such iostat output from a device which can handle only a single queued I/O to the device (eg. IDE driver) and an I/O is stuck. There are 3 more I/Os in the wait queue waiting for the active I/O to complete. The %w and %b are measured as the percent of time during which an I/O was in queue. The svc_t is 0 because the I/O is not finished.
By default, most of the drivers will retry I/Os which don't seem to finish, but the retry interval is often on the order of 60 seconds. If a retry succeeds, then no message is logged to syslog, so you might not see any messages. But just to be sure, what does fmdump (and fmdump -e) say about the system? Are messages logged in /var/adm/messages? -- richard Joe Little wrote: > 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? > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss > _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
