Arch Linux

speedospin

Member

Registered: 2014-06-22

Posts: 3

mount bcache device from live usb

Hello.
Is there any way to mount bcache device from live usb. I use ubuntu as live env and installed bvache-tools. lsblk gives me

sdd                   8:48   0 931.5G  0 disk 
├─sdd1                8:49   0  1007K  0 part 
└─sdd2                8:50   0 931.5G  0 part 
  ├─vg0-home (dm-0) 252:0    0   100G  0 lvm  
  ├─vg0-var (dm-1)  252:1    0    20G  0 lvm  
  ├─vg0-boot (dm-2) 252:2    0   256M  0 lvm  
  └─vg0-root (dm-3) 252:3    0  29.8G  0 lvm 

But when I try to mount f.e. root, I get:

sudo mount /dev/vg0/root /mnt/
mount: you must specify the filesystem type

Thanks.

OlaffTheGreat

Member

Registered: 2013-06-03

Posts: 107

Re: mount bcache device from live usb

Hi,
with a -t flag ?

# mount -t <FS type> /dev/vg0/root /mnt/

Check the file system type. For a live usb, chances are fat16 or ext2

---

Lenovo Thinkpad x230 i5-3320M 2.6GHz 250GB SSD (M4) 16GB
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speedospin

Member

Registered: 2014-06-22

Posts: 3

Re: mount bcache device from live usb

well, I tried these variants, no success. I think the issues is that vg0-root is bcache device type. F.e. I can mount vg0-boot (which is simple lvm ext4) without any problems. But not vg0-root
To work with bcache devices I did

sudo modprobe bcache
sudo update-initramfs -u
update-initramfs is disabled since running on read-only media

I can't make update-initramfs on livecd
Maybe livecd must have bcache module enabled on boot stage?

OlaffTheGreat

Member

Registered: 2013-06-03

Posts: 107

Re: mount bcache device from live usb

Notive I am not a specialist at all.
However, reading the man mount page, I was thinking about Cache-FS type.
Have you tried one of theese type flags?
nfs, nfs4, adfs, affs, autofs

But from what I read here, it seems indeed, there is supposed to no need of the -t flag...

It is said "the bcache allows one to use an SSD as a read/write cache for another blockdevice". Perhaps in some way, the liveCD has to be recognized as a SSD?

---

Lenovo Thinkpad x230 i5-3320M 2.6GHz 250GB SSD (M4) 16GB
SSD | SeaBIOS | GPT | BTRFS | OpenRC | Xfce4 | Zsh | Tmux | Spacemacs
* "Aware Newbie" *
Ibus IM for language script support (e.g. 日本語 - 中文)

ooo

Member

Registered: 2013-04-10

Posts: 1,638

Re: mount bcache device from live usb

It would be better to use up to date arch iso as your live environment when messing with your arch installation from it.
other distributions/old arch iso may have some outdated system tools or kernel.

although it shouldn't be necessary, did you try registering both your cache and backing devices?

echo /dev/vg0/root > /sys/fs/bcache/register
echo /dev/ur/cache/dev > /sys/fs/bcache/register

that should make the devices show up as /dev/bcache<N>

you can also mount the backing devices without cache by running

echo 1 > /sys/block/sdb/bcache/running
mount /dev/vg0/root /mnt/

Last edited by ooo (2014-06-22 21:29:49)

speedospin

Member

Registered: 2014-06-22

Posts: 3

Re: mount bcache device from live usb

thanks OOO, this solution worked for me