I'm making my way through this:


I've done this successfully a couple of times when working with conventional HDDs but I've recently bought and installed the following SSD:

http://uk.transcend-info.com/Products/No-418 (32GB version)

I've reached the "preparing storage devices" section and the output from my


command is the following:

sda              8:0      1    58.6G   0   disk
--sda1           8:1      1    58.6G   0   part  /run/archiso/boottmnt
sr0              11:0     1    1024M   0   rom
loop0            7:0      0    252.5M  1   loop  /run/archiso/sfs/airootfs
loop1            7:1      0    32G     1   loop
--arch_airootfs  254:0    0    32G     0   dm    /
loop2            7:2      0    256M    0   loop
--arch_airootfs  254:0    0    32G     0   dm    /

I'm booting the arch Linux installation from a 64GB USB stick, hence the first 2 entries.

My question is regarding the 'loop' devices.

Does this output look sensible? I was expecting to see the SSD appear as a single 'sda' device so I'm unsure where to go next. Can I install Arch on one of these loop devices and if so, which one? I assume loop1 but I'd like some sound advice before I continue. Also why are these loop devices all separate? Can anybody shed some concise light on this please?


Use losetup to check what each loop device refers to. Real disks should show up as one of sd[a-z], hd[a-z], vd[a-z], ... or if it's a card reader, maybe mmcblk[0-9]...

Also, smartctl -a $device or hdparm -i $device should list name and type of the disk so you can verify you have the corerect one.

Example for my Crucial M4 64GB:

# hdparm -i /dev/sda


 Model=M4-CT064M4SSD2, FwRev=070H, SerialNo=0000000011290314D973

If the disk does not show up at all, check connectors/cables, try another enclosure, etc. or it may just be incompatible or dead on arrival.

As for the installation procedure, there should not be any difference between HDD / SSD, maybe save for alignment / discard.

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My question is regarding the 'loop' devices.

What you are looking at with lsblk is the complicated mount structure of a running linux live system.

loop0            7:0      0    252.5M  1   loop  /run/archiso/sfs/airootfs

A loop device is only a virtual device - it's main idea is to turn a single big (compressed) file into a filesystem. It should maybe be called "deloop" device.

Above line shows how linux from and on the USB drive has mounted a loop device on point airootfs, under /run, which in turn is a virtual device based on RAM.

findmnt is the utility to get an overview.

The terminology is often unclear. Best consult wikipedia for the concepts. Quick washup:

ssd, hdd: products, not linux "devices". mass storage internal and external. Check dmesg at boot to see how the kernel approaches them. One speaks of "external HDD", or "USB SSD" (meaning external also!): giving info and avoiding the ambiguous term "device".

sda, sdb: recognized and alphabetically numbered disks. Anything more complex than floppy disk needs partitioning:

sda1, sda2: partititions, or block devices to be formatted with a filesystem. Only then your SSD can begin to store files (not just bytes)

Just for illustration: with RAID e.g. you add an extra "volume" level, for added functionality.

And the "famous" dd utility can write to both: disks and partitions. Both are "block devicey" enough.

Careful when you use it! you "only" need it to make a bootable USB drive (or disk)(or stick or pen drive...), and then you have to get that numbering letter "a", "b", "c", ... correct:

dd ... of=/dev/sda  #  This can "wipe" a whole internal disk.
dd ... of=/dev/sdb  #  oops. THIS is the external USB drive attached 

dd ... of=/dev/sda1  # first partition on first disk e.g. rootfs
dd ... of=/dev/sda7  # number seven, could be swap partition 

fdisk -l gives a good list of partitions with their sizes and types per disk. Dont start fdisk interactively just to get that info.

Yes, without that background you will have a hard time installing linux. As I say: the words "ssd" and "device" are often used imprecisely. Now you know better!

The basic concept behind all this is concentrated in the mount command. That is what you want to be able to do, at startup, as sysadmin and as user:

mkdir data-f    # create mountpoint (first time only)
mount /dev/sdf35 data-f

The contents of that sata disk "sdf", partition #35, are now accessible as files: cd data-f; ls; ...

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