moving /gnu to different disk

moving /gnu to different disk

[carl hansen]

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Rather than trying the following, I thought, "Why not ask first?"

Due to the sizes of various hard disks in my machine, I want to move /gnu
to /directoryondifferentdisk/gnu
and then do
mount --bind /directoryondifferentdisk/gnu /gnu

(I have already formed a superstition that
ln -s /directoryondifferentdisk/gnu /gnu
won't work)

I see a vast collection of hard links in /gnu/store/.links...

I forsee problems when copying /gnu, not reproducing hard links
but reproducing the data.

Are my fears founded? How to proceed?
Or better to start over with new installation of gnux and /gnu?

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Re: moving /gnu to different disk

[Leo Famulari]

On Tue, Jan 12, 2016 at 01:39:02PM -0800, carl hansen wrote:
> Rather than trying the following, I thought, "Why not ask first?"
> 
> Due to the sizes of various hard disks in my machine, I want to move /gnu
> to /directoryondifferentdisk/gnu
> and then do
> mount --bind /directoryondifferentdisk/gnu /gnu
> 
> (I have already formed a superstition that
> ln -s /directoryondifferentdisk/gnu /gnu
> won't work)
> 
> I see a vast collection of hard links in /gnu/store/.links...
> 
> I forsee problems when copying /gnu, not reproducing hard links
> but reproducing the data.

You could try moving the data with `rsync --hard-links`. Of course you
should test that it works as expected first or you might end up out of
space on the new device, too!

From the rsync man page:
-H, --hard-links            preserve hard links

Of course, there may be a better solution altogether.

> 
> Are my fears founded? How to proceed?
> Or better to start over with new installation of gnux and /gnu?

Re: moving /gnu to different disk

[Andreas Enge]

On Tue, Jan 12, 2016 at 01:39:02PM -0800, carl hansen wrote:
> I forsee problems when copying /gnu, not reproducing hard links
> but reproducing the data.

You can use rsync with the option "-H" to preserve hard links.

I think your proposed solution with bind mounts will work, but I let
the specialists confirm.

Andreas

Re: moving /gnu to different disk

[carl hansen]

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On Tue, Jan 12, 2016 at 2:29 PM, Andreas Enge <andreas@enge.fr> wrote:

> On Tue, Jan 12, 2016 at 01:39:02PM -0800, carl hansen wrote:
> > I forsee problems when copying /gnu, not reproducing hard links
> > but reproducing the data.
>
> You can use rsync with the option "-H" to preserve hard links.
>
> I think your proposed solution with bind mounts will work, but I let
> the specialists confirm.
>
> Andreas
>
> Thanks, Andreas and Leo, the

rsync -Hav /gnu/ /directoryondifferentdisk/gnu
rm -rf /gnu
mkdir /gnu

mount --bind /directoryondifferentdisk/gnu /gnu

seems to be working perfectly.

I hope this question and answer is put into GUIX faq somehow.

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Re: moving /gnu to different disk

[Ludovic Courtès]

Leo Famulari <leo@famulari.name> skribis:

> On Tue, Jan 12, 2016 at 01:39:02PM -0800, carl hansen wrote:
>> Rather than trying the following, I thought, "Why not ask first?"
>> 
>> Due to the sizes of various hard disks in my machine, I want to move /gnu
>> to /directoryondifferentdisk/gnu
>> and then do
>> mount --bind /directoryondifferentdisk/gnu /gnu
>> 
>> (I have already formed a superstition that
>> ln -s /directoryondifferentdisk/gnu /gnu
>> won't work)
>> 
>> I see a vast collection of hard links in /gnu/store/.links...
>> 
>> I forsee problems when copying /gnu, not reproducing hard links
>> but reproducing the data.
>
> You could try moving the data with `rsync --hard-links`.

In fact you can also omit /gnu/store/.links when copying.  Nothing is
lost by doing so.  This directory simply contains a hash-to-file mapping
used by the deduplication mechanism.

However, make sure do copy /var/guix in addition to /gnu/store!
/var/guix/db/db.sqlite is the database containing meta-data for
/gnu/store, so things will break badly if it’s missing or out-of-sync.

HTH,
Ludo’.

Re: moving /gnu to different disk

[Efraim Flashner]

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On Tue, 12 Jan 2016 13:39:02 -0800
carl hansen <carlhansen1234@gmail.com> wrote:

> Rather than trying the following, I thought, "Why not ask first?"
> 
> Due to the sizes of various hard disks in my machine, I want to move /gnu
> to /directoryondifferentdisk/gnu
> and then do
> mount --bind /directoryondifferentdisk/gnu /gnu
> 
> (I have already formed a superstition that
> ln -s /directoryondifferentdisk/gnu /gnu
> won't work)
> 
> I see a vast collection of hard links in /gnu/store/.links...
> 
> I forsee problems when copying /gnu, not reproducing hard links
> but reproducing the data.
> 
> Are my fears founded? How to proceed?
> Or better to start over with new installation of gnux and /gnu?

When I moved mine from / to a new partition I did `cp -a` and it all worked well.

-- 
Efraim Flashner   <efraim@flashner.co.il>   אפרים פלשנר
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Re: moving /gnu to different disk

[Christopher Allan Webber]

carl hansen writes:

> Rather than trying the following, I thought, "Why not ask first?"
>
> Due to the sizes of various hard disks in my machine, I want to move /gnu
> to /directoryondifferentdisk/gnu
> and then do
> mount --bind /directoryondifferentdisk/gnu /gnu
>
> (I have already formed a superstition that
> ln -s /directoryondifferentdisk/gnu /gnu
> won't work)
>
> I see a vast collection of hard links in /gnu/store/.links...
>
> I forsee problems when copying /gnu, not reproducing hard links
> but reproducing the data.
>
> Are my fears founded? How to proceed?
> Or better to start over with new installation of gnux and /gnu?

On my last machine I started out with a too-small root partition, but I
was installing a lot of guix packages, so I bind-mounted /home/guix-gnu/
to /gnu/ and everything worked great.

Re: moving /gnu to different disk

[Mark H Weaver]

Efraim Flashner <efraim@flashner.co.il> writes:

> On Tue, 12 Jan 2016 13:39:02 -0800
> carl hansen <carlhansen1234@gmail.com> wrote:
>
>> Rather than trying the following, I thought, "Why not ask first?"
>> 
>> Due to the sizes of various hard disks in my machine, I want to move /gnu
>> to /directoryondifferentdisk/gnu
>> and then do
>> mount --bind /directoryondifferentdisk/gnu /gnu
>> 
>> (I have already formed a superstition that
>> ln -s /directoryondifferentdisk/gnu /gnu
>> won't work)
>> 
>> I see a vast collection of hard links in /gnu/store/.links...
>> 
>> I forsee problems when copying /gnu, not reproducing hard links
>> but reproducing the data.
>> 
>> Are my fears founded? How to proceed?
>> Or better to start over with new installation of gnux and /gnu?
>
> When I moved mine from / to a new partition I did `cp -a` and it all worked well.

Yes, and 'cp' is many times faster than rsync.  On one non-trivial test,
I found that it was around 8 times faster.

      Mark