Date: Fri, 11 Mar 2005 17:16:59 -0500 From: "Dan Langille" <dan@langille.org> To: freebsd-scsi@freebsd.org Subject: how does the scsi chain work? Message-ID: <4231D28B.28878.564DFBA1@localhost>
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Hi folks, I added the following devices to my computer, all in one SCSI chain: sa0: <QUANTUM DLT7000 2561> Removable Sequential Access SCSI-2 device sa0: 20.000MB/s transfers (10.000MHz, offset 15, 16bit) sa1 at sym0 bus 0 target 6 lun 0 sa1: <QUANTUM DLT7000 2255> Removable Sequential Access SCSI-2 device sa1: 20.000MB/s transfers (10.000MHz, offset 15, 16bit) sa2 at sym0 bus 0 target 8 lun 0 sa2: <QUANTUM DLT8000 0114> Removable Sequential Access SCSI-2 device sa2: 20.000MB/s transfers (10.000MHz, offset 15, 16bit) Then I decided to do some concurrent testing. See below for details. The goal was really to test filling the tape. This exercises both the drive and the tape (all of which are used). Sometimes a single tar takes nearly 4 hours, sometimes it takes only 75 minutes. My question: It doesn't look like the load is shared evenly. Can someone talk a bit about this? That's a pretty general and wide question, I know... [root@lux:/home/dan] # date && time tar cf /dev/nsa2 /usr && time tar cf /dev/nsa2 /usr && time tar cf /dev/nsa2 /usr && ti me tar cf /dev/nsa2 /usr && time tar cf /dev/nsa2 /usr && time tar cf /dev/nsa2 /usr ; date Fri Mar 11 06:21:43 EST 2005 tar: Removing leading '/' from member names real 220m12.162s user 0m50.408s sys 2m44.906s tar: Removing leading '/' from member names real 91m4.119s user 0m41.729s sys 2m18.968s tar: Removing leading '/' from member names real 108m48.709s user 0m40.250s sys 2m18.423s tar: Removing leading '/' from member names tar: usr/home/bacula-restores/stand/help/html.hlp: Write error real 33m27.426s user 0m10.290s sys 0m37.428s Fri Mar 11 13:55:15 EST 2005 [root@lux:/home/dan] # date && time tar cf /dev/nsa0 /usr && time tar cf /dev/nsa0 /usr && time tar cf /dev/nsa0 /usr && time tar c f /dev/nsa0 /usr && time tar cf /dev/nsa0 /usr && time tar cf /dev/nsa0 /usr ; date Thu Mar 10 22:31:57 EST 2005 tar: Removing leading '/' from member names real 75m15.394s user 0m45.666s sys 2m31.039s tar: Removing leading '/' from member names real 114m5.702s user 0m52.549s sys 2m45.939s tar: Removing leading '/' from member names real 156m18.091s user 0m51.538s sys 2m46.858s tar: Removing leading '/' from member names real 119m48.240s user 0m49.670s sys 2m45.721s tar: Removing leading '/' from member names tar: usr/home/bacula-restores/usr/X11R6/share/locale/bs/LC_MESSAGES: Write error real 195m0.408s user 0m38.779s sys 2m13.158s Fri Mar 11 09:32:26 EST 2005 root@lux:/home/dan] # date && time tar cf /dev/nsa1 /usr && time tar cf /dev/nsa1 /usr && time tar cf /dev/nsa1 /usr && time tar cf /dev/n sa1 /usr && time tar cf /dev/nsa1 /usr && time tar cf /dev/nsa1 /usr ; date Thu Mar 10 22:53:40 EST 2005 tar: Removing leading '/' from member names real 103m35.344s user 0m50.394s sys 2m44.732s tar: Removing leading '/' from member names real 112m40.647s user 0m50.555s sys 2m46.049s tar: Removing leading '/' from member names real 152m45.638s user 0m52.656s sys 2m46.040s tar: Removing leading '/' from member names real 201m0.014s user 0m53.838s sys 2m51.051s tar: Removing leading '/' from member names tar: usr/home/bacula- restores/usr/src/contrib/ncurses/form/fld_link.c: Write error real 93m59.622s user 0m22.483s sys 1m8.356s Fri Mar 11 09:57:41 EST 2005 -- Dan Langille : http://www.langille.org/ BSDCan - The Technical BSD Conference - http://www.bsdcan.org/
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