# Trouble understanding btrfs-replace **URL:** \ **Category:** Applications\ **Created:** [December 15, 2024, 12:51pm UTC](https://forum.endeavouros.com/t/trouble-understanding-btrfs-replace/64480 "2024-12-15T12:51:31Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![magtuired](https://forum.endeavouros.com/user_avatar/forum.endeavouros.com/magtuired/32/12336_2.png) [@magtuired](https://forum.endeavouros.com/u/magtuired)\ **Post date:** [December 15, 2024, 12:51pm UTC](https://forum.endeavouros.com/t/trouble-understanding-btrfs-replace/64480/1 "2024-12-15T12:51:31Z")
I am trying to move my system from an SSD that’s running out of space, onto a larger nvme drive, but I’m having some trouble understanding the syntax of the commands. Would really appreciate some assistance in clearing up my confusion. I created a fat 32 for the ESP on the other drive and used dd to copy everything over. For the rest of the nvme, I made one big btrfs partion. Now, I want to run btrfs-replace and move everything over to the other drive, including the top level of the btrfs system, the timeshift-btrfs snapshots, etc. An exact copy basically. However, I cannot for the life of me understand the syntax for the btrfs-replace command, despsite reading the docs, man pages and countless guides and forum posts. The part that trips me up is this part of the man pages/docs: `start [options] | ` Is `` referring to the path that `` is mounted, or ``? This it the lsblk output for the relevant drives (I want to move everything from /dev/sdc2 to /dev/nvme0n1p2): ```bash sdc 8:32 0 232.9G 0 disk ├─sdc1 8:33 0 511M 0 part /boot/efi └─sdc2 8:34 0 232.4G 0 part /mnt/top-level /var/lib/docker/btrfs /var/cache/pacman/pkg /home / nvme0n1 259:0 0 953.9G 0 disk ├─nvme0n1p1 259:1 0 550M 0 part └─nvme0n1p2 259:2 0 953.3G 0 part ``` Now, thinking that `` refers to `` I wasn’t sure what mountpoint to use, since I have several subvolumes, mounted in different places. See my fstab: ```auto # UUID=FDE3-B78F /boot/efi vfat umask=0077 0 2 UUID=313dc380-0d06-44ec-8652-062bd60bd5c6 / btrfs subvol=@,defaults,noatime,space_cache,noautodefrag,compress=zstd 0 0 UUID=313dc380-0d06-44ec-8652-062bd60bd5c6 /home btrfs subvol=@home,defaults,noatime,space_cache,noautodefrag,compress=zstd 0 0 UUID=313dc380-0d06-44ec-8652-062bd60bd5c6 /var/lib/docker/btrfs btrfs subvol=@docker,defaults,noatime,space_cache,compress=zlib 0 0 UUID=313dc380-0d06-44ec-8652-062bd60bd5c6 /var/cache/pacman/pkg btrfs subvol=@var-cache-pacman-pkg,defaults,noatime,space_cache,noautodefrag,compress=zstd 0 0 tmpfs /tmp tmpfs defaults,noatime,mode=1777 0 0 UUID="51596fec-9d35-4522-87c5-64bacce1314c" /mnt/hdd ext4 defaults,errors=remount-ro 0 2 UUID="92bd7cf2-8b9a-4806-a0d8-4384f5afb5ed" /mnt/newdata ext4 defaults,errors=remount-ro 0 2 ``` When I run btrfs filesystem show, I get: ```auto Label: none uuid: 313dc380-0d06-44ec-8652-062bd60bd5c6 Total devices 1 FS bytes used 167.78GiB devid 1 size 232.39GiB used 232.38GiB path /dev/sdc2 ``` Do I put in /dev/sd2 for the `` part? Or should I use /, or /mnt/top-level where I temporarily mounted /dev/sdc2 - so I could access snapshots in timeshift-bfrfs? Any insight into this would be greatly appreciated, also any tips for how to get the system up and running after I hopefully pull of btrfs-send. * * * On a related note: If I want to send a snapshot or snapshots to another non-BTRFS device, how can I do it? I saw from my research that you can create a file version of a snapshot with [btrfs-send](https://btrfs.readthedocs.io/en/latest/btrfs-send.html), using the -f flag. From my understanding the btrfs snapshot would have to be read-only for this to work. So if I set a snapshot to ro=true, can I just do something like this: ```auto sudo btrfs send -f 2024_12_15-11-00-00 timeshift-btrfs/snapshots/2024-12-15_11-00-00/@/ ``` Where ‘2024\_12\_15-11-00-00’ is the name of the f ile. If so, can I just rsync that file over to another drive? If there were an easy way to send every snapshot in the timeshift-btrfs directory (at the top level of the btrfs system) to a backup directory on a non-btrfs drive, that’d be even better. ---
**Author:** ![BluishHumility](https://forum.endeavouros.com/user_avatar/forum.endeavouros.com/bluishhumility/32/70412_2.png) [@BluishHumility](https://forum.endeavouros.com/u/BluishHumility)\ **Post date:** [December 15, 2024, 4:40pm UTC](https://forum.endeavouros.com/t/trouble-understanding-btrfs-replace/64480/2 "2024-12-15T16:40:17Z")
> [@magtuired](#): > > The part that trips me up is this part of the man pages/docs: > > `start [options] | ` > > Is `` referring to the path that `` is mounted Yes. The man page has a usage example a little further down which may help clear this up for you: ```t EXAMPLES Replacing an online drive with a bigger one Given the following filesystem mounted at /mnt/my-vault Label: 'MyVault' uuid: ae20903e-b72d-49ba-b944-901fc6d888a1 Total devices 2 FS bytes used 1TiB devid 1 size 1TiB used 500.00GiB path /dev/sda devid 2 size 1TiB used 500.00GiB path /dev/sdb In order to replace /dev/sda (devid 1) with a bigger drive located at /dev/sdc you would run the following: btrfs replace start 1 /dev/sdc /mnt/my-vault/ You can monitor progress via: btrfs replace status /mnt/my-vault/ After the replacement is complete, as per the docs at btrfs-filesystem(8) in order to use the entire storage space of the new drive you need to run: btrfs filesystem resize 1:max /mnt/my-vault/ ``` In the example, `/dev/sdc` is the new device. It is replacing `/dev/sda` (which is `devid 1`). The mount point for the old device (which is about to become the mount point for the new device) is `/mnt/my-vault`. It is a little confusing how they use `devid` in the command, but I guess if you have a Btrfs filesystem made up of multiple disks you would need that. In the case of Btrfs filesystems where the whole filesystem is on a single partition (which is probably the most common setup), `devid` is always going to be `1`. So in your case, the replace command would be like this: ```auto btrfs replace start 1 /dev/nvme0n1p2 /mnt/top-level ``` > [@magtuired](#): > > Or should I use /, or /mnt/top-level It doesn’t really matter which mount point you use, as long as it is a valid mount point of the Btrfs filesystem for on `/dev/sdc2`. > [@magtuired](#): > > I saw from my research that you can create a file version of a snapshot with [btrfs-send](https://btrfs.readthedocs.io/en/latest/btrfs-send.html), using the -f flag. > > From my understanding the btrfs snapshot would have to be read-only for this to work. That’s right. Actually, `btrfs send` itself only works with RO snapshots (regardless of the options in use). > [@magtuired](#): > > ```auto > sudo btrfs send -f 2024_12_15-11-00-00 timeshift-btrfs/snapshots/2024-12-15_11-00-00/@/ > > ``` > > Where ‘2024\_12\_15-11-00-00’ is the name of the f ile. If so, can I just rsync that file over to another drive? Looks good to me. Test it out and let us know how it goes. > [@magtuired](#): > > If there were an easy way to send every snapshot in the timeshift-btrfs directory (at the top level of the btrfs system) to a backup directory on a non-btrfs drive, that’d be even better. It seems like writing a small script would be the way to go. Probably only a few lines would be needed. - Timeshift creates the snapshot; - `btrfs send -f` to create a file version of the snapshot; - `rsync` the file to the backup target; - Delete the file version of the snapshot. Or if you want to check out another project, btrbk supports sending snapshot backups to non-Btrfs targets. [https://github.com/digint/btrbk](https://github.com/digint/btrbk) ---
**Author:** ![magtuired](https://forum.endeavouros.com/user_avatar/forum.endeavouros.com/magtuired/32/12336_2.png) [@magtuired](https://forum.endeavouros.com/u/magtuired)\ **Post date:** [December 15, 2024, 5:09pm UTC](https://forum.endeavouros.com/t/trouble-understanding-btrfs-replace/64480/4 "2024-12-15T17:09:47Z")
Thank you for confirming and the tips for backing up snapshots! I ended up trusting my gut and running it pointing at /mnt/top\_level…but it kept unexpectedly cancelling, with journalctl showing that /dev/sdc2 didn’t have enough space, which was confusing to me, because it was showing about 100GB free. I removed some snapshots, but still no luck. Finally figured I could run btrfs balance, which turned out was the solution. Then however I was having issue with grub, tried the old arch-chroot trick (that I’ve had lots of opportunities to practice), but then running grub-install kept telling me it couldn’t find the efi…turns out after much too much trial and error I realised I should have mounted the first partition as /mnt/boot/efi not /mnt/efi. 😅 I’d like to say this took me only a few hours, but this whole process has taken me the better of two days! Now what to do with the smaller drive…I’d like to use it for my Steam library maybe…but I’m wondering if btrfs would have any benefits there, or if good old ext4 will do. It’s certainly simpler… ---
**Author:** ![system](https://forum.endeavouros.com/uploads/default/original/2X/9/9ea52f9fd5ef8e609e593c362d61a36295f48be8.png) [@system](https://forum.endeavouros.com/u/system)\ **Post date:** [December 17, 2024, 5:10pm UTC](https://forum.endeavouros.com/t/trouble-understanding-btrfs-replace/64480/5 "2024-12-17T17:10:00Z")
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