how to properly mount an external usb hard drive & other questions

how to properly mount an external usb hard drive & other questions

[dhan.war]

hi all

i am using up to date debian sid with xfce desktop environment. i am 
using Linux 3.13-rc6-amd64 #1 SMP Debian 3.13~rc6-1~exp1 (2013-12-30) 
x86_64 GNU/Linux from experimental.
i have installed usbmount to auto mount all the devices connected 
through USB.

[cmd# 1] i have created btrfs partition on my external USB hard drive 
using the following command :

# mkfs.btrfs -f -L btrfs -m single /dev/sdc
Turning ON incompat feature 'extref': increased hardlink limit per file 
to 65536
fs created label btrfs on /dev/sdc
	nodesize 16384 leafsize 16384 sectorsize 4096 size 931.51GiB
Btrfs v3.12

[cmd# 2] my permissions of the device :
# ls -l /dev/sdc
brw-rw---- 1 root floppy 8, 32 Jan  5 09:47 /dev/sdc

my questions :
[a] does the partition created by me is appropriate ?
[b] how do i specify lzo compression in fstab ? last time when i tried 
to create entry fstab it is complaining about the auto mounting of the 
device by automount.
[c] what compression method is used by btrfs by default for the 
partitions created using the command mentioned above. [ cmd# 1]
[d] does the file permissions for my device are accurate ? [ cmd# 2]
[e] what is the appropriate fstab entry for my device ? [ i don't want 
to remove usbmount].
[f] should i use single or dup for the device ?

please provide suggestions for configuring my device appropriately. 
thank you for reading the message patiently.

please alway cc me.

regards,
wardhan.

Re: how to properly mount an external usb hard drive & other questions

[Justus Seifert]

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On 05.01.2014 05:34, dhan.war wrote:
> hi all
> 
> i am using up to date debian sid with xfce desktop environment. i am
> using Linux 3.13-rc6-amd64 #1 SMP Debian 3.13~rc6-1~exp1 (2013-12-30)
> x86_64 GNU/Linux from experimental.
> i have installed usbmount to auto mount all the devices connected
> through USB.
> 
> [cmd# 1] i have created btrfs partition on my external USB hard drive
> using the following command :
> 
> # mkfs.btrfs -f -L btrfs -m single /dev/sdc
> Turning ON incompat feature 'extref': increased hardlink limit per file
> to 65536
> fs created label btrfs on /dev/sdc
>     nodesize 16384 leafsize 16384 sectorsize 4096 size 931.51GiB
> Btrfs v3.12
> 
> [cmd# 2] my permissions of the device :
> # ls -l /dev/sdc
> brw-rw---- 1 root floppy 8, 32 Jan  5 09:47 /dev/sdc
> 
> my questions :
> [a] does the partition created by me is appropriate ?

it seems ok

> [b] how do i specify lzo compression in fstab ? last time when i tried
> to create entry fstab it is complaining about the auto mounting of the
> device by automount.

if you dont want the partition to be mounted with the fstab during boot
then you should add "noauto" to the list of options in the respective
fstab line.

> [c] what compression method is used by btrfs by default for the
> partitions created using the command mentioned above. [ cmd# 1]

none.  if you order mount to use compression without spezifieng the
algo, it will use zlib (thats like gz).  if you do not use the option
"compression" then it will not compress new files.

> [d] does the file permissions for my device are accurate ? [ cmd# 2]

i dont know.  are you member of the group floppy?  what is the purpose
of the group floppy on your machine?  what users are members of the
group floppy?

> [e] what is the appropriate fstab entry for my device ? [ i don't want
> to remove usbmount].

/dev/sdc /path/to/your/favorite/mountpoint/that/has/to/exist/already
btrfs compress,noauto 0 0

> [f] should i use single or dup for the device ?

maybe use single

> 
> please provide suggestions for configuring my device appropriately.
> thank you for reading the message patiently.
> 
> please alway cc me.
> 
> regards,
> wardhan.


i tried to keep it short.  feel free to ask for more.

cheers
justus

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Re: how to properly mount an external usb hard drive & other questions

[Justus Seifert]

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On 05.01.2014 18:43, Justus Seifert wrote:
> On 05.01.2014 05:34, dhan.war wrote:
>> hi all
>>
>> i am using up to date debian sid with xfce desktop environment. i am
>> using Linux 3.13-rc6-amd64 #1 SMP Debian 3.13~rc6-1~exp1 (2013-12-30)
>> x86_64 GNU/Linux from experimental.
>> i have installed usbmount to auto mount all the devices connected
>> through USB.
>> […]
>>
>> [e] what is the appropriate fstab entry for my device ? [ i don't want
>> to remove usbmount].
> 
> /dev/sdc /path/to/your/favorite/mountpoint/that/has/to/exist/already
> btrfs compress,noauto 0 0

oh i forgot: if you want to mount it without su privileges you have to use:
/dev/sdc /path/to/your/favorite/mountpoint compress,noauto,users,user 0 0

also look into subvolume mounting with "subvol=myfirstsubvolume" in your
list of mount options, if you want to do cool stuff with subvolumes.



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Re: how to properly mount an external usb hard drive & other questions

[Jim Salter]

On 01/05/2014 12:50 PM, Justus Seifert wrote:
> oh i forgot: if you want to mount it without su privileges you have to 
> use:
>
> /dev/sdc /path/to/your/favorite/mountpoint compress,noauto,users,user 0 0
If you want LZO compression, as you specified:

           /dev/sdc /path/to/mountpoint compress=lzo,noauto,users,user 0 0

Better yet, if your btrfs is actually on /dev/sdc right now, let's get 
that fstab entry mounting it by UUID instead.

           ls -l /dev/disk/by-uuid | grep sdc
           lrwxrwxrwx 1 root root 10 Jan  3 09:40 
12345678-9abc0-1234-5678-9a0123456789 -> ../../sdc

So then:

           # this is not a real UUID, you need to check 
/dev/disk/by-uuid on your machine for a real UUID
           UUID=12345678-9abc0-1234-5678-9a0123456789 
/path/to/mountpoint   compress=lzo,noauto,users,user   0   0

This is EXTRA important with a USB drive, since it's HIGHLY likely it 
won't always be on the same physical devicename.

Re: how to properly mount an external usb hard drive & other questions

[Jim Salter]

On 01/05/2014 01:02 PM, Jim Salter wrote:
> If you want LZO compression, as you specified:
>
>           /dev/sdc /path/to/mountpoint compress=lzo,noauto,users,user 0 0
>
> Better yet, if your btrfs is actually on /dev/sdc right now, let's get 
> that fstab entry mounting it by UUID instead.
>
>           ls -l /dev/disk/by-uuid | grep sdc
>           lrwxrwxrwx 1 root root 10 Jan  3 09:40 
> 12345678-9abc0-1234-5678-9a0123456789 -> ../../sdc
>
> So then:
>
>           # this is not a real UUID, you need to check 
> /dev/disk/by-uuid on your machine for a real UUID
>           UUID=12345678-9abc0-1234-5678-9a0123456789 
> /path/to/mountpoint   compress=lzo,noauto,users,user   0   0
>
> This is EXTRA important with a USB drive, since it's HIGHLY likely it 
> won't always be on the same physical devicename.

One other note: in this particular case, you might actually be better 
served setting compression by mounting the drive normally, then:

          cd /path/to/drive
          chattr +c . ; chattr +c * ; chattr +c .*

This will set compression on by default for any future files stored on 
that USB drive, *without* needing any special mount options.

Why might this be a better idea? Well, if it's a USB drive, presumably 
you might want to mount it on foreign systems from time to time. This 
way, even if you mount the drive on a foreign system that doesn't know 
anything about your preferences, it will see the +c on the root 
directory of the drive, and store any new data on the drive compressed.

The only caveat: +c won't set the compression algorithm to LZO. It'll be 
gzip, which is the default algorithm. (And, of course, this won't 
compress any EXISTING data already stored there - only NEW data written 
to it after you set the +c attribute.)