Fibre Channel part 2

Saturday, October 7, 2006

524 bytes per sector on a harddisk? That may work for some IBM RAID array, but FreeBSD isn't going to stand for it. After some searching, it appears the thing to do is to somehow change the sector size and do a low-level format.

Turns out Seagate has a very detailed manual on these drives, and it mentions that the sector size can be between 512 and 528 bytes. The sector size setting is apparently stored on a "SCSI mode page" 3, and the FreeBSD camcontrol utility has support for viewing/editing this. Running

camcontrol modepage da0 -m 3

shows:

Tracks per Zone:  7564 
Alternate Sectors per Zone:  0
Alternate Tracks per Zone:  20
Alternate Tracks per Logical Unit:  0
Sectors per Track:  784
Data Bytes per Physical Sector:  524
Interleave:  1
Track Skew Factor:  272 
Cylinder Skew Factor:  120
SSEC:  0
HSEC:  1
RMB:  0
SURF:  0

which is the current settings, and the same command with the addition of -P 2 to view the default settings shows:

Tracks per Zone:  7564
Alternate Sectors per Zone:  0
Alternate Tracks per Zone:  20
Alternate Tracks per Logical Unit:  0
Sectors per Track:  809
Data Bytes per Physical Sector:  512
Interleave:  1
Track Skew Factor:  272
Cylinder Skew Factor:  120
SSEC:  0
HSEC:  1
RMB:  0
SURF:  0

Those settings would be ideal. Notice how the smaller sector size gives more sectors per track. How to get the drive to switch to them? Adding a -e parameter to the camcontrol command as in: camcontrol modepage da0 -m 3 -e should allow for changing that modepage, but all I got back was: camcontrol: no editable entries. Running camcontrol modepage da0 -m 3 -P 1 to see the changeable values shows:

Tracks per Zone:  0
Alternate Sectors per Zone:  0
Alternate Tracks per Zone:  0
Alternate Tracks per Logical Unit:  0
Sectors per Track:  0
Data Bytes per Physical Sector:  0
Interleave:  0
Track Skew Factor:  0
Cylinder Skew Factor:  0
SSEC:  0
HSEC:  0
RMB:  0
SURF:  0

Dang, the IBM firmware has locked out making changes to the sector size. According to the Seagate manual:

The changeable values list can only be changed by downloading new firmware into the flash E-PROM.

Oh crap, where do you get new firmware, and how would you load it? Doesn't seem that Seagate has new firmware available for easy download (like you get with motherboards and such). Doing some digging with Google turned up some potential sources from deep within Sun and Grass Valley Group websites, but for all I know they're non-standard similar to how the IBM stuff is. This was not looking good.

Some more digging turned up this thread from a FreeBSD mailing list, which suggests setting a sector-size value and immediately reformatting the disk with:

camcontrol cmd da1 -v -c "15 10 0 0 v:i1 0" 12 -o 12 "0 0 0 8  0 0:i3 0 v:i3" 512
camcontrol cmd -n da -u 1 -v -t 7200 -c "4 0 0 0 0 0"

I wasn't sure if this was applicable to my particular FC drive, and would just changing the sector size also adjust the sectors-per-track or other possibly related settings? After doing a lot of reading on the camcontrol command, and various SCSI specs, I felt I had some understanding of what the above commands did, and figured it was worth a shot.

What do you know, it worked! There was a bit of trouble with the second camcontrol command in that it timed out too soon, but the sector size did change and it stayed changed. For my second drive, I tried the regular camcontrol format command instead of the raw one given in the example above.

camcontrol cmd da0 -v -c "15 10 0 0 v:i1 0" 12 -o 12 "0 0 0 8  0 0:i3 0 v:i3" 512
camcontrol format da0

That actually worked a bit better, because camcontrol format shows a nice progress display, instead of making you guess a timeout and waiting for while you hope it's working.

So now I've got a couple 10K rpm FC drives with FreeBSD installed and booting off them.

da0 at isp0 bus 0 target 120 lun 0
da0: <IBM-SSG S0BE146 3706> Fixed Direct Access SCSI-3 device 
da0: 100.000MB/s transfers, Tagged Queueing Enabled
da0: 140014MB (286749488 512 byte sectors: 255H 63S/T 17849C)
da1 at isp0 bus 0 target 124 lun 0
da1: <IBM-SSG S0BE146 3709> Fixed Direct Access SCSI-3 device 
da1: 100.000MB/s transfers, Tagged Queueing Enabled
da1: 140014MB (286749488 512 byte sectors: 255H 63S/T 17849C)

I noticed the smaller sector size gives more total space on the drive. They're fairly fast, but not life-changingly fast. It's been an interesting experience messing with them, but next time around I'll probably go back to SATA drives (or maybe SAS will be cheap on eBay by then....)