44 lines
1.4 KiB
Markdown
44 lines
1.4 KiB
Markdown
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---
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layout: post
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title: "Mount a Zvol under linux"
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date: 2024-01-12
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comments: true
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tags: zfs, zvol, mount, kpartx, linux, nixos
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---
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Zvol are volumes backed by a zfs pool. They are quite popular as vm disk images.
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Sometimes you just want to examine them in the host; here is how to mount them.
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When the pool is imported, they show up under `/dev/zvol/<path to zvol
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dataset>`. At this point they are just raw drives, and kernel knows nothing
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about its structure. To be able to mount them, we first need to read its
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partition structure and create partition specific `/dev/` entires with
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`kpartx(8)`[^1].
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```shell
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# -a for add
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kpartx -a /dev/zvol/<pathtozvol>
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```
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This will create corresponding devices for partitions under `/dev/mapper`
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```
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$:/dev/mapper]# ls -al
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total 0
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drwxr-xr-x 2 root root 120 Jan 12 17:04 .
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drwxr-xr-x 20 root root 3980 Jan 12 17:04 ..
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crw------- 1 root root 10, 236 Jan 12 17:00 control
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lrwxrwxrwx 1 root root 7 Jan 12 17:04 root-zvol1 -> ../dm-0
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lrwxrwxrwx 1 root root 7 Jan 12 17:04 root-zvol2 -> ../dm-1
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lrwxrwxrwx 1 root root 7 Jan 12 17:04 root-zvol3 -> ../dm-2
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```
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Now you can mount them as a regular disk with `mount`.
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```
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mount /dev/mapper/root-zvol1 /mnt
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```
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[^1]: In nixos, `kpartx` is part of package [`multipath-tools`](https://search.nixos.org/packages?channel=23.11&show=multipath-tools&from=0&size=50&sort=relevance&type=packages&query=kpartx)
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