Re: [gentoo-user] LVM and moving things around

[Wol]

On 27/03/2022 21:13, Dale wrote:
> Wol wrote:
>> On 27/03/2022 20:17, Dale wrote:
>>> Howdy,
>>>
>>> I sort of started this on another thread but wanted to nail a few things
>>> down first.  I'm wanting to encrypt some parts of my data on /home.
>>> This is what I got hard drive wise.
>>>
>>>
>>> root@fireball / # pvs
>>>     PV         VG     Fmt  Attr PSize    PFree
>>>     /dev/sda7  OS     lvm2 a--  <124.46g 21.39g
>>>     /dev/sdb1  Home2  lvm2 a--    <5.46t     0
>>>     /dev/sdc1  Home2  lvm2 a--    <7.28t     0
>>>     /dev/sdd1  Home2  lvm2 a--    <7.28t     0
>>>     /dev/sde1  backup lvm2 a--   698.63g     0
>>> root@fireball / #
>>>
>> One big piece of missing information. What does fdisk say about
>> sd[b,c,d]1? And can you add sdf1?
>
> I have the entire drive as one large partition for each drive.  I could
> have done it as a whole device but I wanted partitions to give a hint
> that the drive is in use, if booted from other medium for example.
>
> I have enough extra space that I can remove either a 6TB or a 8TB
> drive.  Once that is done, I can start to encrypt and move data around.
> This is some additional info from df for /home:
>
>
> /dev/mapper/Home2-Home2     20T  8.7T   12T  45% /home
>
>
> If I remove a 8TB drive, I'd still have enough room for my data.  I
> could then rebuild /home starting with the 8TB drive just freed up.
> Then as I move data, I could expand them one at a time encrypting as I
> go.  I'd rather not have to buy a hard drive right now.  Tight budget
> given other things I got going on.  I do have backups, more than one in
> a couple important data spots.
>
Do you need to shrink your fs first though?

My three 3TB partitions are raided, and /dev/md/home is my PV. I've only 
allocated the space to LVs that they need, so I could probably shrink 
the PV and remove a drive without needing to mess about with my LVs at 
all. I get the impression you may have allocated all your space, not a 
good idea.

My attitude is my data is backed up, expanding an LV/FS is low risk, 
I'll just grow stuff as I need to ... my /home partition contains proper 
home drives, things like videos may be in /home/videos, but they're 
actually a separate partition, etc etc.
>
>>
>> I'm guessing you've got three 8TB drives? Or is it two 8s and a 6? Can
>> you get a third 8TB? And if you're encrypting *parts* of /home ...
>> what parts?
>>>
>>> I've done some checking on sizes of things I want to encrypt and am
>>> weighing options.  I use LVM which should help make things easier.  I've
>>> downloaded and printed some howtos regarding shrinking the file system
>>> and LVM thingys.  It seems I need to shrink the file system while my
>>> /home partition is unmounted.  Then move the data off whichever drive I
>>> want to remove and then remove the drive itself.  After that I can
>>> encrypt the just removed drive and start moving files over, using rsync
>>> is my plan.  I think that is the basic steps.
>>
>> Not necessarily.
>>>
>>> My question now comes to this.  When I encrypt one of the drives, can I
>>> then expand that drive with it being encrypted or is that not a option?
>>> I plan to encrypt two of the drives as one volume group and leave one
>>> other volume group as normal.  I just want to be sure whether or not I
>>> can expand a encrypted LVM drive the same as a normal LVM since both
>>> uses LVM.  I use cryptsetup commands to accomplish the encryption if
>>> that matters.  So as a example, I start with one 7TB drive encrypted,
>>> move some data to it, then want to add either the 5TB or 7TB drive.  Can
>>> I just expand it like a normal LVM or does it being encrypted change
>>> things?
>>>
>>> Thoughts?  My remove steps look sensible?  Expanding encrypted LVM
>>> possible?
>>
>> If you are using LVM to do the encryption, then I can't see any
>> problems adding a new PV to an encrypted VG.
>>>
>>> Dale
>>>
>> Personally, I'd use dm-crypt to encrypt the drive, and then the whole
>> lot is encrypted, and put plain LVM over that. I've got dedicated
>> layers for everything.
>>
>> It looks like your home2 is 6TB+8TB+8TB. I'd get a new 8TB, put
>> dm-crypt on it, and add it. Now I can remove the first 8TB, dm-crypt
>> it and re-add it. Same with the second 8TB. Now remove the 6TB and
>> there you are ...
>>
>> My layout's rather different from yours, so I don't think I ought to
>> say too much :-)
>>
>> Cheers,
>> Wol
>>
>>
>
>
> What is the advantage of dm-crypt over cryptsetup?  I've learned how to
> use cryptsetup with my external drive so was hoping to stick with what I
> already know.  Unless there is a advantage to dm-crypt.
>
I don't know either. I'm just far more familiar with the dm/md layer 
because I run md-raid over dm-integrity. Hence dm-crypt.

Is cryptsetup a layer in its own right, or part of lvm? I prefer the 
Unix "use several tools each of which does one thing well", other people 
prefer a swiss army knife like ZFS or btrfs. I don't know where 
cryptsetup lies on that spectrum, and I don't know your preferences on 
that spectrum.

Cheers,
Wol