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 Gonz?lez" <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) -----------------------------
On 07/31/2017 08:50 AM, Fred Smith wrote:> 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 Gonz?lez" <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? > >I agree with fred .. this would OVERWRITE empty space with zeros and remove it .. that MIGHT be something you would do for security because it would replace what was on there before. But it would not free up any space and should not impact your backup at all (if you are backing up files). -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 198 bytes Desc: OpenPGP digital signature URL: <http://lists.centos.org/pipermail/centos/attachments/20170731/fdfcf125/attachment-0001.sig>
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 Gonz?lez" <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) ----------------------------- _______________________________________________ CentOS mailing list CentOS at centos.org https://lists.centos.org/mailman/listinfo/centos
If you are using XFS - there is mount option "discard|nodiscard"
From XFS man page:
discard|nodiscard
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.
Vladimir
-----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 Gonz?lez" <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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https://lists.centos.org/mailman/listinfo/centos
_______________________________________________
CentOS mailing list
CentOS at centos.org
https://lists.centos.org/mailman/listinfo/centos
On Jul 31, 2017, at 7:50 AM, Fred Smith <fredex at fcshome.stoneham.ma.us> wrote:> > On Mon, Jul 31, 2017 at 08:28:49AM -0500, Leroy Tennison wrote: >> dd to totally fill the partition > > I may be blind, but I don't seehow that technique can "reclaim" any space.In addition to the OP?s qemu case, zeroing the free space can also be valuable when building binary OS images from physical media. The first time you do it with a fresh drive, the disk image contains only what you put onto the drive. Then later when you update that drive for the next release, you cause files to be overwritten, thus leaving outdated copies of file system blocks laying around which you don?t want to be dd?d into the resulting disk image. Zeroing the free space not only prevents inclusion of these discarded FS blocks, they compress better, too.
Once upon a time, Warren Young <warren at etr-usa.com> said:> Zeroing the free space not only prevents inclusion of these discarded FS blocks, they compress better, too.Check out the "virt-sparsify" command - it does all of this for you. -- Chris Adams <linux at cmadams.net>