discard support

[Vasiliy Tolstov]

Hello, as i see you switched to ext4, why you not enable by default
discard option? For thin provisioned storage this is very useful
option.


--
Vasiliy Tolstov,
e-mail: v.to...@selfip.ru
jabber: va...@selfip.ru

[Ilya Dmitrichenko]

Vasiliy, may be you could give some background with pros/cons of that ext4 feature, either in your own words or by pointing to some docs that you have read on this?

[Vasiliy Tolstov]

2015-03-25 13:23 GMT+03:00 Ilya Dmitrichenko <errorde...@gmail.com>:
> Vasiliy, may be you could give some background with pros/cons of that ext4
> feature, either in your own words or by pointing to some docs that you have
> read on this?

You can google discard ssd thin provision and other things, In two
words - discard under virtual machines brings ability to free space on
host when file deleted inside vm.
Without this option used space does not freed when file deleted inside vm.

[Ilya Dmitrichenko]

Ok, but does that work on all hypervisors?

[Vasiliy Tolstov]

2015-03-25 13:27 GMT+03:00 Ilya Dmitrichenko <errorde...@gmail.com>:
> Ok, but does that work on all hypervisors?

If this is not supported by hypervisor it silently dropped.

[Vasiliy Tolstov]

2015-03-25 13:46 GMT+03:00 Vasiliy Tolstov <v.to...@selfip.ru>:
> If this is not supported by hypervisor it silently dropped.

But if coreos team provide flags for enabling discard on all devices
this is very useful for me =)

[Michael Marineau]

IIRC some implementations of discard/trim can impair performance if
done as part of normal filesystem operations. On those systems a
periodic call to fstrim to do the cleanup as a batch job is more
appropriate. If you wish to use the runtime discard feature in ext4
you can create a /etc/fstab that looks something like the following:

LABEL=ROOT / ext4 discard 0 1