Date: Fri, 13 Aug 1999 11:00:55 -0600 (MDT) From: "Kenneth D. Merry" <ken@kdm.org> To: mwm@phone.net (Mike Meyer) Cc: freebsd-stable@FreeBSD.ORG Subject: Re: On freezes in 3.2-Stable Message-ID: <199908131700.LAA61444@panzer.kdm.org> In-Reply-To: <Pine.BSF.4.10.9908122141570.94664-100000@guru.phone.net> from Mike Meyer at "Aug 12, 1999 09:45:55 pm"
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Mike Meyer wrote... > On Fri, 13 Aug 1999, W Gerald Hicks wrote: > :->When I kept up with the numbers for these things in a former > :->life working for a disk manufacturer, I was always astounded > :->at how much current the drives pulled during their power-on > :->sequence. After startup, current begins to taper off rapidly. > > This stopped being relevant a long time ago, but... > > DEC MIPS-based workstations worked around this problem by having > tweaked PROMs on their SCSI drives, with a SPIN-UP-ON-POWERON bit that > defaulted to off. Ultrix would send the drives the SCSI command to > spin them up - *after* everything else in the system was powered > on. This meant they could use a cheaper power supply, as no supported > configuration required it to deal with more than one drive spinning up > at a time. > > Dealing with this was the *least* of the problems in trying to use DEC > SCSI drives on other platforms. But they could be made to work. Most disks have a jumper that disables power-on spinup. Believe it or not, we've got something similar to the Ultrix spin-up stuff. FreeBSD/CAM will spin up drives on boot that are not already spinning. Generally, this happens in the probe stage, at the serial number inquiry stage. Most disks will not return a serial number without being spun up. Some disks, most notably high end IBM disks, will return their serial number without being spun up. So the boot process goes on in that case, and the drives are spun up when the da driver sends its read capacity command. By default, CAM will only attempt to spin up 4 drives at a time, to avoid overloading a power supply. You can adjust the maximum number of concurrent start unit commands allowed with the CAM_MAX_HIGHPOWER kernel config option. Ken -- Kenneth Merry ken@kdm.org To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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