Re: Poor SCSI disk preformance [more on camcontrol please!]

2004-01-06 Thread Derek Marcotte 
 Aha.  Check the WCE bit to see if your write cache is enabled
on the
 disk

Bingo:

# dd if=/dev/zero of=/dev/da0 bs=64k 
[1] 2253
# iostat -K -w 1 da0
  tty da0 cpu
 tin tout  KB/t tps  MB/s  us ni sy in id
   2   38  0.00   0  0.00   1  0  1  0 98
   0   43 64.00 223 13.91   0  0  8  1 91
   0   43 64.00 223 13.92   0  0  5  0 95
   0   43 64.00 223 13.92   0  0  8  1 91
   0   43 64.00 223 13.92   0  0  6  0 94
   0   42 64.00 223 13.92   0  0  5  1 94
   0   43 64.00 223 13.92   1  0  6  1 92

 Set it by running cmcontrol mode da0 -m 8 -e -P 2, and set
WCE: 1

I needed to modify your command slightly to:
camcontrol mode da0 -m 8 -e -P 0

I guess I don't have a page 2 for some reason...  This will
probably cause this bit to be reset on reboot as well, because it
is the current page?

Is it prudent to attempt to set the WCE:1 on all drives that get
attached?  I will be formatting a large number of greatly varying
drives, including ATA converted to SCSI type drives, and really
old, and really new drive types.

I've had a look at man camcontrol earlier, but I don't know
enough about the inner workings of SCSI for this to mean much to
me.  It seems to be pretty obscure (like how would I know to
enable features/specs to edit a modepage?), but extremely
powerful.  Where can I read more about this, is there a good
camcontrol FAQ/tutorial out there that explains what these
details actually mean/do?

Thanks for the help!
Derek

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Re: Poor SCSI disk preformance [more on camcontrol please!]

2004-01-06 Thread Dan Nelson 
In the last episode (Jan 06), Derek Marcotte said:
  Aha.  Check the WCE bit to see if your write cache is enabled on
  the disk
 
 Bingo:
 
 # dd if=/dev/zero of=/dev/da0 bs=64k 
 # iostat -K -w 1 da0
   tty da0 cpu
  tin tout  KB/t tps  MB/s  us ni sy in id
0   43 64.00 223 13.92   1  0  6  1 92
 
 I guess I don't have a page 2 for some reason...  This will probably
 cause this bit to be reset on reboot as well, because it is the
 current page?

Possibly.  Power the drive off and see if the change sticks. :)

 Is it prudent to attempt to set the WCE:1 on all drives that get
 attached?  I will be formatting a large number of greatly varying
 drives, including ATA converted to SCSI type drives, and really
 old, and really new drive types.

I've never seen WCE hurt sequential write access, so it's probably safe
to turn on.  If you're paranoid about possibly getting damaged
filesystems during power outages, you might want to turn it back off,
although every year or so there's a thread that pops up debating its
merits.
 
 I've had a look at man camcontrol earlier, but I don't know
 enough about the inner workings of SCSI for this to mean much to
 me.  It seems to be pretty obscure (like how would I know to
 enable features/specs to edit a modepage?), but extremely
 powerful.  Where can I read more about this, is there a good
 camcontrol FAQ/tutorial out there that explains what these
 details actually mean/do?

Everything under camcontrol modepage and cmd is pretty much
straight from the SCSI spec.  You can buy copies of it from ANSI (I
think you can download draft copies from www.t10.org somewhere), and
sometimes disk vendors will ship copies with vendor-specific info. 
About 15 years ago, I bought a Maxtor disk that didn't include the
little sheet saying which jumpers were which SCSI id.  I called up and
asked them to send me a copy, and they sent me the whole reference
manual for the drive, detailing every SCSI command and modepage.

-- 
Dan Nelson
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