[CentOS] claiming unsused space back

Mon Jul 31 14:54:27 UTC 2017
Ruttkay Vladimir <vladimir.ruttkay at telekom.sk>

If you are using XFS - there is mount option "discard|nodiscard"

From XFS man page:

              Enable/disable the issuing of commands to let the block device reclaim space freed by the filesystem.  This is useful for SSD devices, thinly provisioned LUNs and virtual machine images, but may have a performance impact.

              Note:  It  is  currently  recommended that you use the fstrim application to discard unused blocks rather than the discard mount option because the performance impact of this option is quite severe.  For this reason, nodiscard is the default.


-----Original Message-----
From: CentOS [mailto:centos-bounces at centos.org] On Behalf Of Leroy Tennison
Sent: Monday, July 31, 2017 4:42 PM
To: centos <centos at centos.org>
Subject: Re: [CentOS] claiming unsused space back

You're right, there's a procedure following it, once the space is zeroed qemu-img will recognize it as such and will eliminate it when 'convert' is used.  Apparently Fedora qemu has some better capabilities to shrink partitions but they haven't made it to "long term support" distributions yet.  For now, what has to be done to shrink qcow[2] partitions (raw works) is (regardless of client OS, for Windows defragment is first used followed by resizing the partitions in Disk Management then finally Sysinternals' sdelete to zero disk space - I have used this process and it works but with surprises): defragment (even Linux, look into e2defrag, shake, a defrag script or e4defrag - can be found on the web, haven't used them, YMMV), zero disk space, resize the partition, then use qemu-img to convert to raw (or even qcow - it works).  However, to permanently resize you must convert to raw, shrink and re-convert to qcow2 if you want those capabilities.

----- Original Message -----
From: "Fred Smith" <fredex at fcshome.stoneham.ma.us>
To: "centos" <centos at centos.org>
Sent: Monday, July 31, 2017 8:50:57 AM
Subject: Re: [CentOS] claiming unsused space back

On Mon, Jul 31, 2017 at 08:28:49AM -0500, Leroy Tennison wrote:
> I realize this is wandering off-topic but, if you have found Debian commands, you're doing better than me.  What are they?  Also, are you allowing dd to totally fill the partition (what I have found on the web as a recommendation)?  If so, is the OS surviving acceptably?
> ----- Original Message -----
> From: "Miguel González" <miguel_3_gonzalez at yahoo.es>
> To: "centos" <centos at centos.org>
> Sent: Saturday, July 29, 2017 5:11:33 AM
> Subject: [CentOS] claiming unsused space back
> Hi,
>  I´m running a CentOS server in a VPS. Backups of the VPS take quite
> much space if I don´t claim unused space.
>  Currently I´m using dd if=/dev/zero of=/mytempfile and remove that file
> to claim that unused space. Any automatic way of doing a similar thing
> in CentOS? I have googled for it but I have only found Debian commands.
>  Thanks in advance!

I may be blind, but I don't seehow that technique can "reclaim" any space.
all it does is fill up all the space not allocated to other files by creating
one large file that occupies all otherwise unused disk space.

presumably you'll delete that file once it is created, but you won't have
any more free disk space than you had before. the only difference will be
that that unused space will then be filled with zeroes.

what are you actually wanting to do here?

---- Fred Smith -- fredex at fcshome.stoneham.ma.us -----------------------------
                      The eyes of the Lord are everywhere, 
                    keeping watch on the wicked and the good.
----------------------------- Proverbs 15:3 (niv) -----------------------------
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