Hard Disk device IDs in Linux

Dan Egli ddavidegli at gmail.com
Thu Mar 7 22:31:40 MST 2013


*I've got a question. Someone asked me this the other day and I honestly
couldn't answer them. It's not a situation that one normally comes across,
but I must admit my curiosity is piqued! :)*

* *

*How does Linux handle device IDs for hard disks in excess of 26? I know
the first hard disk is /dev/sda, the second is /dev/sdb, and so forth. But
the English alphabet is only 26 letters. That means that hard disk 26 would
be /dev/sdz. What about any more than that, as might be found in some of
the larger rack mount servers in the 7U and 8U size range? They have 28 and
32 drives respectively (usually, I know some have more or less, but that's
a good average). Does Linux simply fail to address anything above drive
#26? Or does it move to capital letters (i.e. /dev/sdA)? Or perhaps it's
double letters (/dev/sdaa)?  *

* *

*Like I said, I admit it's an unusual question, but the lack of an answer
is kind of getting to me. Perhaps someone here has an answer?*

* *

*Oh, by the way. On the same token, anyone aware of any limitation on the
number of drives that can be connected to a single software raid array in
Linux? I.e. if I have an 8U case with 32 hard disk drives, could I make a
single /dev/md0 with all 32 drives as members? Something like a raid 6?*

* *

*Thanks in advance folks!*

* *

*--- Dan*


More information about the PLUG mailing list