Am 17.10.2016 um 03:50 schrieb Qu Wenruo:
> At 10/17/2016 02:54 AM, Stefan Priebe - Profihost AG wrote:
>> Am 16.10.2016 um 00:37 schrieb Hans van Kranenburg:
>>> On 10/15/2016 10:49 PM, Stefan Priebe - Profihost AG wrote:
>>>> cp --reflink=always takes sometimes very long. (i.e. 25-35 minutes)
>>>> An example:
>>>> source file:
>>>> # ls -la vm-279-disk-1.img
>>>> -rw-r--r-- 1 root root 204010946560 Oct 14 12:15 vm-279-disk-1.img
>>>> target file after around 10 minutes:
>>>> # ls -la vm-279-disk-1.img.tmp
>>>> -rw-r--r-- 1 root root 65022328832 Oct 15 22:13 vm-279-disk-1.img.tmp
>>> Two quick thoughts:
>>> 1. How many extents does this img have?
>> filefrag says:
>> 1011508 extents found
> Too many fragments.
> Average extent size is only about 200K.
> Quite common for VM images, if not setting no copy-on-write (C) attr.
> Normally it's not a good idea to put VM images into btrfs without any
Those are backups just written sequentially once. As far as i know the
extent size is hardcoded to 128k for compression. Isn't it?
>>> 2. Is this an XY problem? Why not just put the img in a subvolume and
>>> snapshot that?
>> Sorry what's XY problem?
>> Implementing cp reflink was easier - as the original code was based on
>> XFS. But shouldn't be cp reflink / clone a file be nearly identical to a
>> snapshot? Just creating refs to the extents?
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