3

Running lsblk (an excellent command for getting info about the disk configuration from within scripts and OS-agnostic high-level languages) on Fedora 29 like so:

$ lsblk --output NAME,FSTYPE,ROTA,PARTTYPE,TYPE,RAND,TRAN

NAME                   FSTYPE            ROTA PARTTYPE TYPE  RAND TRAN
sda                                         0          disk     0 sata
├─sda1                 ext4                 0 0x83     part     0 
└─sda2                 LVM2_member          0 0x8e     part     0 
  ├─fedora_root        ext4                 0          lvm      0 
  └─fedora_swap        swap                 0          lvm      0 
sdb                                         0          disk     0 sata
└─sdb1                 ext4                 0 0x83     part     0 
sdc                                         1          disk     1 sata
└─sdc1                 linux_raid_member    1 0xfd     part     1 
  └─md127              crypto_LUKS          1          raid1    0 
    └─luks_mdraid      ext4                 1          crypt    0 
sdd                                         1          disk     1 sata
└─sdd1                 linux_raid_member    1 0xfd     part     1 
  └─md127              crypto_LUKS          1          raid1    0 
    └─luks_mdraid      ext4                 1          crypt    0 

Here we have asked for the following (the list of available columns can be obtained by issuing lsblk --help):

  • NAME : device name (nicely arranged in a tree)
  • FSTYPE : filesystem type
  • ROTA : is this a "rotational device" (spinning rust, DVD etc.)
  • PARTTYPE : partition type UUID (values one sets in fdisk)
  • TYPE : device type
  • RAND : "adds randomness"
  • TRAN : device transport type

Ok, so the device "adds randomness" as per RAND. But in what context? And to what value? It seems to have something to do with the device being "rotational". What does "adds randomness" mean?

3

A "1" in the RAND column means the device driver for the device adds randomness to the kernel's random number generator. This random number generator produces random numbers that can be read from the /dev/random special file. The disk drive device driver uses timing variations as the source for randomness. These timing variations are hard to predict especially on mechanical drives.

  • 1
    Indeed, and it's a toggle. It's displaying the toggle /sys/block/DEV/queue/add_random described there queue-sysfs.txt – A.B Apr 21 at 13:01
-3

As stated RAND adds randomness (another output column), whose values are the flags which shows if Memory access in that specific block is random or not, with 0 means no Random memory access and 1 flag means otherwise. Generally, Regular Memory Access causes Latency in memory access, hence Random Memory Access is favored.

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