qubes-doc/configuration/disk-trim.md
2017-05-11 18:48:59 +10:00

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---
layout: doc
title: Disk TRIM
permalink: /doc/disk-trim/
redirect_from:
- /en/doc/disk-trim/
- /doc/DiskTRIM/
- /wiki/DiskTRIM/
---
VMs have already TRIM enabled by default, but dom0 doesn't. There are some security implications (read for example [this article](https://asalor.blogspot.com/2011/08/trim-dm-crypt-problems.html)), but IMO not very serious.
To enable TRIM in dom0 you need to:
1. Get your LUKS device UUID:
~~~
ls /dev/mapper/luks-*
~~~
2. Add entry to `/etc/crypttab` (replace luks-\<UUID\> with the device name and the \<UUID\> with UUID alone):
~~~
luks-<UUID> UUID=<UUID> none allow-discards
~~~
3. Add `rd.luks.allow-discards=1` to kernel cmdline (`/etc/default/grub`, GRUB\_CMDLINE\_LINUX line)
4. Rebuild grub config (`grub2-mkconfig -o /boot/grub2/grub.cfg`)
5. Rebuild initrd **in hostonly mode**:
~~~
dracut -H -f
~~~
6. Add "discard" option to `/etc/fstab` for root device
7. Reboot the system, verify that allow-discards is really enabled (`dmsetup table`)
There is a [bug affecting allow-discards option](https://bugzilla.redhat.com/show_bug.cgi?id=890533), once it will be fixed, first two steps will be no longer needed.