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DiskTRIM changed

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Marek Marczykowski-Górecki 2014-05-11 16:03:56 +00:00
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---
layout: wiki
title: DiskTRIM
permalink: /wiki/DiskTRIM/
---
VMs have already TRIM enabled by default, but dom0 doesn't. There are some security implications (read for example [​this article](http://asalor.blogspot.com/2011/08/trim-dm-crypt-problems.html)), but IMO not very serious.
To enable TRIM in dom0 you need:
1. Get your root device UUID:
``` {.wiki}
blkid /dev/mapper/*root
```
2. Add entry to `/etc/crypttab` (replace \<UUID\> with the device UUID):
``` {.wiki}
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**:
``` {.wiki}
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.