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SDNick484
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PostPosted: Sun Jan 06, 2013 11:06 pm    Post subject: Best Way To Move An Existing Install Between Drives? Reply with quote

What's the best way to migrate an existing Gentoo install between two drives? My laptop (Lenovo T400) currently has a 60GB SSD, and I picked up a much newer 120GB SSD that I'd like to move my install to. Am I better off doing a dd from one drive to the other then growing the file system, or should I do a copy? Any other thoughts or suggestions? I realize I could do a fresh install on my new drive, but I'm pretty happy with the current state and don't want to have to recompile everything. In case it matters, my laptop has a second disk drive bay instead of an optical drive, so I shouldn't be too limited in terms of bus speed.
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The Doctor
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PostPosted: Sun Jan 06, 2013 11:33 pm    Post subject: Reply with quote

I believe your best course of action is to partition your new drive, mount any partitions and copy. I believe dd is very bad for SSDs because it copies everything, include empty disk space. The extra writes are, of course, bad for the SSD. Make sure your preserve your permissions when you copy (cp -ax / /mnt/newDisk). -a to preseve premissions, x to avoid coping the new disk and /proc to the new disk. more ideas on this here

Chroot and install your boot loader and you should be good to go.

NOTE: Backups are good, especially when messing with your entire system.
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PostPosted: Mon Jan 07, 2013 1:24 am    Post subject: Reply with quote

tar is preferred over "cp -a" because it handles hard links properly, and also because the "-a" switch is not available on many non-GNU platforms.

You would do something like this to copy files properly using tar:

Code:
# tar -cvf - / | ( cd /mnt/backup && tar -xvf - )


Alternatively, if you have rsync installed (as every Gentoo does), you can just use "rsync -a".

But, as The Doctor says, you should have full backups anyway, You can read about my method for regular backups.
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Last edited by Hypnos on Tue Jan 08, 2013 6:22 pm; edited 1 time in total
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SDNick484
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PostPosted: Mon Jan 07, 2013 2:29 am    Post subject: Reply with quote

Ah yes, rsync is a good suggestion, I will likely go that route. How well are hard links handled in rsync? On this laptop I don't have many hard links that I created myself, so it would only be ones generated by the OS/portage. My concern with a tarpipe was that the buffer size would severely limit the transfer rate.

I do have backups of all the data/media that I care about, but that's primarily limited to /home. I guess I should also back up /etc since it's fairly small and would compress very well. My concern with doing a fresh install of Gentoo on the new drive and just restoring is that I'd lose a lot of stuff that isn't portaged maintained. For example, I have a 32bit Debian chroot environment that I'd need to re-create. Also this install is a few years old and has packages no longer in portage that I still occasionally used. It's all stuff I could re-create if I really wanted to, but I'd rather not waste the time if I don't have to.
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Hypnos
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PostPosted: Mon Jan 07, 2013 3:48 am    Post subject: Reply with quote

SDNick484 wrote:
Ah yes, rsync is a good suggestion, I will likely go that route. How well are hard links handled in rsync? On this laptop I don't have many hard links that I created myself, so it would only be ones generated by the OS/portage.

To copy hard links as hard links pass the "-H" switch to rsync.

Quote:
My concern with a tarpipe was that the buffer size would severely limit the transfer rate.

The SSDs may be fast enough for this to be a bottleneck, but that's something you can test with large test files.

Quote:
I do have backups of all the data/media that I care about, but that's primarily limited to /home. I guess I should also back up /etc since it's fairly small and would compress very well. My concern with doing a fresh install of Gentoo on the new drive and just restoring is that I'd lose a lot of stuff that isn't portaged maintained. For example, I have a 32bit Debian chroot environment that I'd need to re-create. Also this install is a few years old and has packages no longer in portage that I still occasionally used. It's all stuff I could re-create if I really wanted to, but I'd rather not waste the time if I don't have to.

I back up my home directory every day, /etc every week, and everything else (except certain temporary directories) once a month. This way if I have a hard disk failure or a laptop theft I'll not lose any time to rebuilding necessary things, nor lament lost emails or family photos.
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d2_racing
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PostPosted: Mon Jan 07, 2013 4:24 am    Post subject: Reply with quote

I use rsync to switch my hardware.

I upgraded from a HDD to SSD with Rsync.
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cwr
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PostPosted: Tue Jan 08, 2013 9:08 am    Post subject: Reply with quote

I've always used tar to copy filesystems as Hypnos suggested, except that I also use the p flag.
It's always worked, but there are other methods; I wouldn't use dd if I were you, since it copies
junk as well as files and needs either exact partition matching or a certain amount of tinkering.

(Definitely back up /etc, which is a pain to re-create; also /boot and /lib/modules, and /home
of course).

Will
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SDNick484
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PostPosted: Tue Jan 08, 2013 6:20 pm    Post subject: Reply with quote

Thanks again for the suggestions. I ended up going the rsync route and so far, so good. I was getting 60+MB/s after I disabled compression (limited by the slower SSD).

The exact string I ended up using was:
# rsync -av --exclude '/mnt/newroot' --exclude '/proc' --exclude '/dev' --exclude '/sys' --exclude '/net' --exclude '/lost+found' --exclude '/run' / /mnt/newroot

I should also mention I had /boot mounted under /mnt/newroot/boot, and while the contents copied fine, I forgot I had to re-run grub to install the new MBR on it. Fortunately I was able to boot off the old drive in the second drive bay to quickly make the fix.
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Wallsandfences
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PostPosted: Tue Jan 08, 2013 10:29 pm    Post subject: Reply with quote

There is a little script called mkstage4.sh around (google it...) that does what it's called after. (Nearly) no settings or options are wanted, and it works at the actual /
It's basically a tar-command with some nice tricks and ideas.

Rüdiger
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cach0rr0
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PostPosted: Fri Jan 11, 2013 5:52 am    Post subject: Reply with quote

Wallsandfences wrote:
There is a little script called mkstage4.sh around (google it...) that does what it's called after. (Nearly) no settings or options are wanted, and it works at the actual /
It's basically a tar-command with some nice tricks and ideas.

Rüdiger


should be findable here, that is, once gentoo-wiki.com comes back online - http://en.gentoo-wiki.com/wiki/Custom_Stage4

still available in google cache.

that's the method I've been using for some time now. So far so good.
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SDNick484
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PostPosted: Fri Jan 11, 2013 6:38 am    Post subject: Reply with quote

Thanks, good to know about that mkstage4.sh for future reference.
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toralf
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PostPosted: Fri Jan 11, 2013 2:19 pm    Post subject: Reply with quote

Use the adviced tar command + the tar option "-p" to preserve file attributes.
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