36

Let’s say I have 50 USB flash drives.

I assume they get to be /dev/sda to /dev/sdz. What comes after /dev/sdz?

3
  • Extension of the same question - what happens with virtual xvd devices like /dev/xvda ? NVME devices of the format /dev/nvme1n1 or with partiiton nvme2n1p3 Does the old format IDE driver giving /dev/hda device nodes have the same limits ?
    – Criggie
    Apr 1, 2022 at 23:05
  • 3
    Amusingly, I once tried to help a Windows user who had run out of drive letters. This was years ago. He had two floppies, several compressed drives (each uses two drive letters), external drives and several CD-ROMs and DVDs. Drive A: to drive Z: is all you get.
    – Wastrel
    Apr 2, 2022 at 14:17
  • @Wastrel At that point you start mounting additional volumes under directories. Yes, that is a very *nix-like approach. Works fine. The underlying physical device paths are numerical, so it'll happily keep incrementing forever (\Device\HardDisk1, etc.).
    – Bob
    Apr 3, 2022 at 15:17

1 Answer 1

61

It will go to /dev/sdaa, /dev/sdab, /dev/sdac, etc.

Here is a comment from the source code:

/**
 *  sd_format_disk_name - format disk name
 *  @prefix: name prefix - ie. "sd" for SCSI disks
 *  @index: index of the disk to format name for
 *  @buf: output buffer
 *  @buflen: length of the output buffer
 *
 *  SCSI disk names starts at sda.  The 26th device is sdz and the
 *  27th is sdaa.  The last one for two lettered suffix is sdzz
 *  which is followed by sdaaa.
 *
 *  This is basically 26 base counting with one extra 'nil' entry
 *  at the beginning from the second digit on and can be
 *  determined using similar method as 26 base conversion with the
 *  index shifted -1 after each digit is computed.
 *
 *  CONTEXT:
 *  Don't care.
 *
 *  RETURNS:
 *  0 on success, -errno on failure.
 */

https://github.com/torvalds/linux/blob/master/drivers/scsi/sd.c#L3303-L3324

9
  • 7
    I wonder how many SCSI devices one would need to attach to reach /dev/sdeignfully?
    – Tom
    Apr 1, 2022 at 1:49
  • 7
    @Tom you'd have to connect 2061986601 devices (tenderleo.gitbooks.io/leetcode-solutions-/content/GoogleEasy/…)
    – alexyorke
    Apr 1, 2022 at 6:55
  • 3
    @Tom why sdeignfully?
    – user253751
    Apr 1, 2022 at 9:40
  • 4
    @user253751, one presumes because that's the first English word beginning sd that contains "full" within it. Apr 1, 2022 at 10:54
  • 7
    @user253751 Longest word in my en-US wordlist (~275k entries) that begins with "sd".
    – Tom
    Apr 1, 2022 at 17:16

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