Date: Thu, 18 Mar 2010 11:41:38 -0400 From: Glen Barber <glen.j.barber@gmail.com> To: scsi@freebsd.org Subject: Optimum dev_openings value Message-ID: <20100318154138.GA30096@orion.hsd1.pa.comcast.net>
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Hi, I have three machines running 8.0-RELEASE, each with two mirrored Seagate SCSI disks using ZFS. In making sure these machines are performing as best as possible, I'm trying to find what the best practices are with regards to dev_openings values, and what determines the default dev_openings value. Two machines have identical ahc(4) Adaptec AIC7899 Ultra160 SCSI adapters, but display different defaults, which I have not had luck finding an explanation: h04# camcontrol tags da0 -v (pass0:ahc1:0:0:0): dev_openings 33 (pass0:ahc1:0:0:0): dev_active 0 (pass0:ahc1:0:0:0): devq_openings 33 (pass0:ahc1:0:0:0): devq_queued 0 (pass0:ahc1:0:0:0): held 0 (pass0:ahc1:0:0:0): mintags 2 (pass0:ahc1:0:0:0): maxtags 255 h21# camcontrol tags da0 -v (pass0:ahc0:0:0:0): dev_openings 64 (pass0:ahc0:0:0:0): dev_active 0 (pass0:ahc0:0:0:0): devq_openings 64 (pass0:ahc0:0:0:0): devq_queued 0 (pass0:ahc0:0:0:0): held 0 (pass0:ahc0:0:0:0): mintags 2 (pass0:ahc0:0:0:0): maxtags 255 h04# camcontrol devlist <SEAGATE ST318406LC 0109> at scbus1 target 0 lun 0 (pass0,da0) <SEAGATE ST318406LC 010A> at scbus1 target 1 lun 0 (pass1,da1) h21# camcontrol devlist <SEAGATE ST3146855LC 0003> at scbus0 target 0 lun 0 (pass0,da0) <SEAGATE ST3146855LC 0003> at scbus0 target 1 lun 0 (pass1,da1) Is there an obvious explanation for the difference here? The third machine uses sym(4), which I expect would cause a different default dev_openings (currently defaulted to 44). Is there a general rule to adjusting this value? -- Glen Barber
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