Name of disk

sim085 · 09-01-2017, 04:14 AM

Hello, when I use fdisk -l I get a list of all disks currently plugged in. These disks are given names such as /dev/sda, /dev/sdb, /dev/sdc, etc... However I noticed that the same disk does not always come with the same name, for example I have an 80GB disk which sometimes comes up as /dev/sdd, and sometimes as /dev/sde,

Is this normal? What determines the name given to a drive?

Also is there a better method than looking at the size of the disk to determine which name corresponds to which physical disk?

pan64 · 09-01-2017, 04:53 AM

yes, most probably it is normal.
The detection process itself will give the names, this reflects to the order of the detection.
You can name your partitions, and you can use partitions by their names or by their uuids. They will not be changed at all.
see /dev/disk

Shadow_7 · 09-01-2017, 05:12 AM

Normal == Yes

It's kind of determined by which powers up first and gets recognized by the OS. I have an older system with PATA and SATA drives and the /dev/ names flip flop all the time. So use LABELs or UUIDs in your /etc/fstab and bootloader.

allend · 09-01-2017, 06:30 AM

Quote:

Also is there a better method than looking at the size of the disk to determine which name corresponds to which physical disk?

Try running 'blkid' with root privileges.

sim085 · 09-01-2017, 09:05 PM

I formatted all my disks and deleted all partitions, how can I force the OS to always recognise my Toshiba disk as /dev/sda and my WD disks as /dev/sdb, etc?

Is there an example I can follow?

Quote:

Originally Posted by Shadow_7

Normal == Yes

It's kind of determined by which powers up first and gets recognized by the OS. I have an older system with PATA and SATA drives and the /dev/ names flip flop all the time. So use LABELs or UUIDs in your /etc/fstab and bootloader.

jefro · 09-01-2017, 09:30 PM

https://wiki.archlinux.org/index.php..._device_naming

I assume your distro will have some data on these types of naming schemes. What is your distro?

Shadow_7 · 09-02-2017, 06:30 AM

$ cat /etc/fstab

Code:

# 
# /etc/fstab: static file system information
#
# <file system>	<dir>	<type>	<options>	<dump>	<pass>

UUID=22222222-2222-2222-2222-222222222222 / ext4 defaults,noatime 0 1

$ cat /boot/grub/grub.cfg | grep UUID

Code:

     linux /boot/vmlinuz-linux root=UUID=22222222-2222-2222-2222-222222222222 acpi=force acpi_backlight=vendor modeset

Various means to "customize" your UUIDs. tune2fs, xfs_admin, ... Or set it at the point of creation. I tend to use a YYYYMMDD-HH00-PPPP-PPPP-PPPPPPPPPPPP format where YYYY is year, M month, D day, H hour, and P is the partition number. It makes it easier to type if I have to type it manually in grub.cfg or from grubs command line mode "c". Plus a visual reference of how LONG AGO I did this install. Basically replace /dev/AAA# with a UUID=..., as long as the fstab and boot loader know what's up, it just works. Caveat, install grub AFTER you setup /etc/fstab. Or you might find yourself updating grub.cfg a bit too much manually. And re-install grub if you change the UUID.

As far as customizing /dev/ names to device, udev kind of does that. But if you can't boot linux in the first place, you don't get to udev to customize things. So relatively useless for booting names.

pan64 · 09-02-2017, 06:53 AM

Quote:

Originally Posted by sim085

I formatted all my disks and deleted all partitions, how can I force the OS to always recognise my Toshiba disk as /dev/sda and my WD disks as /dev/sdb, etc?

Is there an example I can follow?

we were trying to explain, it is not possible, you need to use UUID or labels instead of /dev/sda /dev/sdb ...
But probably there is a way (I don't know about).

JeremyBoden · 09-02-2017, 10:30 AM

Usually

sda corresponds to SATA1, sdb corresponds to SATA2 etc.
But it's not gauranteed.

Code:

ls -l /dev/disk/by-uuid

should give something like

Code:

lrwxrwxrwx 1 root root 10 Sep  2 12:09 11169433-051f-4b3b-bd05-7c31c85f0d47 -> ../../sdb2
lrwxrwxrwx 1 root root 10 Sep  2 12:09 2549555d-63e6-48fc-b2d1-3072ef81c4d6 -> ../../sda4
lrwxrwxrwx 1 root root 10 Sep  2 12:09 5A8C-B187 -> ../../sdb1
lrwxrwxrwx 1 root root 10 Sep  2 12:09 7081860c-6dd6-41d2-9fdb-0734b73b8c47 -> ../../sdb3
lrwxrwxrwx 1 root root 10 Sep  2 12:09 7197cd12-815e-4190-b552-c3d6c0c2f24c -> ../../sda2
lrwxrwxrwx 1 root root 10 Sep  2 12:09 91B7-FE06 -> ../../sda1
lrwxrwxrwx 1 root root 10 Sep  2 12:09 b554d17c-7d66-477b-b8a2-1e0233ef1329 -> ../../sda3
lrwxrwxrwx 1 root root 10 Sep  2 12:09 fd2d39a7-5feb-48c5-ad61-a1a361e18bd8 -> ../../sda5

Note that UUID's are given in UUID sequence & that UUID's of FAT partitions are much shorter.

rknichols · 09-02-2017, 11:56 AM

Quote:

Originally Posted by JeremyBoden

Usually

sda corresponds to SATA1, sdb corresponds to SATA2 etc.
But it's not gauranteed.

And, it can change just because you happened to have a USB drive connected while booting. It's just not reliable, and can bite you in very bad ways (e.g., booting with your backup drive connected and then writing to the wrong drive because the drive designations were different from usual).