Re: Accepting discard to free space from disk images

[Roman Mamedov <rm@romanrm.net>]

On Mon, 9 Feb 2015 20:42:56 +0500
Roman Mamedov <rm@romanrm.net> wrote:

> On Mon, 09 Feb 2015 10:26:33 -0500
> "Devon B." <devon.b@virtualcomplete.com> wrote:
> 
> > If you don't mind me asking, what version kernel are you running and are 
> > you using any special mount options?
> 
> Well actually I did not claim I have working discard through 'loop', but your
> post made me curious.
> 
> $ sudo dd if=/dev/zero of=100g bs=1M seek=100000 count=1
> 1+0 records in
> 1+0 records out
> 1048576 bytes (1.0 MB) copied, 0.00221052 s, 474 MB/s
> 
> $ sudo mkfs.ext4 100g
> [...]
> 
> $ du -hsc 100g 
> 133M	100g
> 133M	total
> 
> $ sudo mount -o loop 100g /mnt/tmp1/
> 
> (then in a new terminal window):
> $ cd /mnt/tmp1/
> $ df -h .
> Filesystem      Size  Used Avail Use% Mounted on
> /dev/loop0       96G   60M   92G   1% /mnt/tmp1
> $ sudo dd if=/dev/zero of=zerofile bs=1M count=1024
> 1024+0 records in
> 1024+0 records out
> 1073741824 bytes (1.1 GB) copied, 0.944377 s, 1.1 GB/s
> $ sync
> 
> (back to the original one):
> $ du -hsc 100g 
> 1.2G	100g
> 1.2G	total

> (2nd window):

Forgot to add I also did 'rm zerofile' here, of course.

> $ sudo fstrim .
> 
> (back to the original one):
> $ du -hsc 100g 
> 133M	100g
> 133M	total
> 
> So it does work for me just fine even with 'loop'.
> Kernel version 3.14.32, mount options
> rw,noatime,nodiratime,compress=zlib,space_cache,inode_cache.
> 


-- 
With respect,
Roman