What's the difference between /dev/dsk and /dev/sda?

itsmarziparzi

5/21/24, 10:44 AM

I was researching about block devices and character devices. I found an article that mentions how block devices are assigned as /dev/sd[a-z]. But then I read a different article that mentions how block devices are assigned as /dev/dsk/[c#t#d#]. Are they not both block devices? When is one used over the other?

2 + 3

filesystems

Gerald Schneider

5/21/24, 11:28 AM

It would be helpful if you would share the article where you found the nominations.

Luuk

5/21/24, 2:57 PM

You can check if it is a block device by executing `file /dev/dsk/*`

Nikita Kipriyanov

6/2/24, 8:56 AM

Also it would be nice if you explain which OS you are thinking of. /dev/sdX hints at Linux, but I can't remember seeing /dev/dsk there, usually there is /dev/disk. On the other hand, HP-UX has /dev/dsk/cXtYdZ, but no /dev/sdX. Maybe you mixed two different articles about two different systems?

Score:2

Server

Gerald Schneider

5/21/24, 11:27 AM

/dev/sd[a-z] is the most common naming scheme for hard disks in Linux.

Other Unix flavours use different naming schemes, you can find /dev/dsk/ for example in HPUX or Solaris.

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Score:0

Server

HBruijn

5/21/24, 11:13 AM

Some naming conventions are the result of how the kernel discovers devices, the first SCSI/SATA/SAS Disk gets the name sda allocated and the second scb and subsequent letters fo the alphabet are used for other disks.

Other device drives use different block device naming schemes for the devices they detect.

The problem with discovery is that discovery can fail, for example your first disk fails and then the second disk can get the name sda allocated, while before it was named sdb. An /etc/fstab entry for sdb1 won't work anymore, but the data isn't gone, but now sda1 needs to be mounted on that mount point.

To counter that persistent device naming schemes have been created, which can be used to identify a device correctly, even when discovery assigns it a different name. That are for example the /dev/disk/by-uuid/* and/or /dev/disk/by-label/* device names.

Some more background here: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/managing_storage_devices/assembly_overview-of-persistent-naming-attributes_managing-storage-devices

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Elon Musk

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EN: What's the difference between /dev/dsk and /dev/sda?

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