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March 11, 2005

Disk Device Names (Solaris)

Last week, I mentioned a typical disk name as being something like c0t0d0s0. A reader wanted to know if there was any significance to the components of this name...

Believe it or not, there is some meaning and it is sort of historical. It reads (left to right) as C(ontroller) zero, T(arget) zero, D(isk) zero, S(lice) zero. Note that this is going from the largest to the smallest component. A normal Sun server has at least one controller (c0) but may have more. Each controller can have multiple targets. The number of targets is related to the type of the controller (normally SCSI). An IDE controller only has two targets (0 and 1). SE (Single Ended SCSI) normally has 7. Differential, Wide, Ultra, LVD SCSI all have more.

Technically a target can relate to multiple disks. These disks would share the same target number but have different offsets. I have seen this but it would be more than 15 years ago. Modern disk subsystems do not normally use this (unless you are mapping a SAN and using virtual disk numbers and even then it is more usual to fiddle the target numbers). The place where it still occurs is in low-end tape libraries. These may have a single SCSI target but then sub-numbers (disk numbers) for the drive itself, the library controller and possibly the auto-loader.

Finally we have the slice - Sun allow for 8 slices (0..7) but one of these is reserved (slice 2) for the whole disk. More on that next week...

Posted by Ozguru at March 11, 2005 06:00 AM


You're such a geek! :-)

Posted by: Cindy at March 11, 2005 06:03 AM

I feel that I should apologise for being a geek... unfortunately I can't seem to help it. I tried going to Geeks Anonymous but it didn't help much...

Posted by: Ozguru at March 11, 2005 06:03 AM