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Old 01-14-2009, 12:36 AM
Paul E Condon
 
Default Question about LVM and volume images on loop

I want to allocate several large blank files on HD,
and make them into virtual hard disk which I mount
using loop.

I then want to treat them as 'physical volumes' under
LVM, and collect them into a single volume group.

Then, I intend to define a few larger logical volumes
on this 'volume group'. I do this because I want to
store large files on a HD whose hardware interface
limits file sizes to 4Gb, and I want to store larger
files than 4Gb. ( The HD has 500Gb total capacity.)

My problem is that I can't figure out how to execute
pvcreate on my 'image physical volumes'. If I mount
the image, I think I should apply pvcreate to
/dev/loopxx, but that doesn't work, giving a message
that the volume is mounted. If I unmount the image,
I get (blk0 is my file to be initialized) :

big:/media/WDP-5/blks# pvcreate -f blk0
Device blk0 not found (or ignored by filtering).

How can I associate a loop device node with a particular
file, without mounting it? Or how can I get pvcreate
to write whatever it puts on a phisical volume into
a file on disk? Or how can I mount a loop device without
specifing a fils system type? Or, etc.?

TIA
--
Paul E Condon
pecondon@mesanetworks.net


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Old 01-14-2009, 01:08 AM
Jeff D
 
Default Question about LVM and volume images on loop

On Tue, 13 Jan 2009, Paul E Condon wrote:

> I want to allocate several large blank files on HD,
> and make them into virtual hard disk which I mount
> using loop.
>
> I then want to treat them as 'physical volumes' under
> LVM, and collect them into a single volume group.
>
> Then, I intend to define a few larger logical volumes
> on this 'volume group'. I do this because I want to
> store large files on a HD whose hardware interface
> limits file sizes to 4Gb, and I want to store larger
> files than 4Gb. ( The HD has 500Gb total capacity.)

Maybe I'm missing something here, but how is the hardware interface
stopping you from writing files larger than 4G? That's just something I
haven't ran into. How is the drive formatted now? Can't you just format
the drive with ext3 or something else that supports large files? I don't
think that LVM is going to solve your problem here though.

Jeff

--
8 out of 10 Owners who Expressed a Preference said Their Cats Preferred Techno.


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Old 01-14-2009, 01:33 AM
"Boyd Stephen Smith Jr."
 
Default Question about LVM and volume images on loop

On Tuesday 2009 January 13 19:36:22 Paul E Condon wrote:
>I do this because I want to
>store large files on a HD whose hardware interface
>limits file sizes to 4Gb, and I want to store larger
>files than 4Gb. ( The HD has 500Gb total capacity.)

HD hardware interfaces do not know where files begin and end.[1] You *might*
be using a filesystem that limits you to 4Gb. If so, LVM won't buy you
anything and you'll have to switch filesystems.
--
Boyd Stephen Smith Jr. ,= ,-_-. =.
bss@iguanasuicide.net ((_/)o o(\_))
ICQ: 514984 YM/AIM: DaTwinkDaddy `-'(. .)`-'
http://iguanasuicide.net/ \_/

[1] How could they? Each filesystem stores files differently. Also, mdadm
and LVM between the physical drives and the filesystem would change that.
 
Old 01-14-2009, 04:18 AM
Paul E Condon
 
Default Question about LVM and volume images on loop

On Tue, Jan 13, 2009 at 06:08:05PM -0800, Jeff D wrote:
> On Tue, 13 Jan 2009, Paul E Condon wrote:
>
> > I want to allocate several large blank files on HD,
> > and make them into virtual hard disk which I mount
> > using loop.
> >
> > I then want to treat them as 'physical volumes' under
> > LVM, and collect them into a single volume group.
> >
> > Then, I intend to define a few larger logical volumes
> > on this 'volume group'. I do this because I want to
> > store large files on a HD whose hardware interface
> > limits file sizes to 4Gb, and I want to store larger
> > files than 4Gb. ( The HD has 500Gb total capacity.)
>
> Maybe I'm missing something here, but how is the hardware interface
> stopping you from writing files larger than 4G? That's just something I
> haven't ran into. How is the drive formatted now? Can't you just format
> the drive with ext3 or something else that supports large files? I don't
> think that LVM is going to solve your problem here though.
>

Yes, it's not hardware. Truth is it's vfat. I have had difficulty with
Western Digital USB HD when I try to reformat tham for ext3, and they
special software from WD to rewrite the vfat format. A software overlay
seemed a good way to go. I'm still hoping.

--
Paul E Condon
pecondon@mesanetworks.net


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Old 01-14-2009, 04:23 AM
Paul E Condon
 
Default Question about LVM and volume images on loop

On Tue, Jan 13, 2009 at 08:33:46PM -0600, Boyd Stephen Smith Jr. wrote:
> On Tuesday 2009 January 13 19:36:22 Paul E Condon wrote:
> >I do this because I want to
> >store large files on a HD whose hardware interface
> >limits file sizes to 4Gb, and I want to store larger
> >files than 4Gb. ( The HD has 500Gb total capacity.)
>
> HD hardware interfaces do not know where files begin and end.[1] You *might*
> be using a filesystem that limits you to 4Gb. If so, LVM won't buy you
> anything and you'll have to switch filesystems.

My hope is that I can write a bunch of 4G files mount them as 4G hard drives,
and group them into a single 'volume group' whose total capacity is some large
multiple of 4G. Is this impossible?

--
Paul E Condon
pecondon@mesanetworks.net


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Old 01-14-2009, 05:27 AM
"Boyd Stephen Smith Jr."
 
Default Question about LVM and volume images on loop

On Tuesday 13 January 2009, Paul E Condon <pec@mesanetworks.net> wrote
about 'Re: Question about LVM and volume images on loop':
>On Tue, Jan 13, 2009 at 08:33:46PM -0600, Boyd Stephen Smith Jr. wrote:
>> On Tuesday 2009 January 13 19:36:22 Paul E Condon wrote:
>> >I do this because I want to
>> >store large files on a HD whose hardware interface
>> >limits file sizes to 4Gb, and I want to store larger
>> >files than 4Gb. ( The HD has 500Gb total capacity.)
>>
>> HD hardware interfaces do not know where files begin and end.[1] You
>> *might* be using a filesystem that limits you to 4Gb. If so, LVM won't
>> buy you anything and you'll have to switch filesystems.
>
>My hope is that I can write a bunch of 4G files mount them as 4G hard
> drives, and group them into a single 'volume group' whose total capacity
> is some large multiple of 4G. Is this impossible?

It's probably a bad idea. BUT, it should be possible.

It would be much better to use ext[234], jfs, xfs, or even reiserfs
directly on the drive. You say you have problems, but I'm using reiserfs
across a raid-0 on WD driver and reiserfs across a raid-1 on WD drives
without issues. Could you go into more details.
--
Boyd Stephen Smith Jr. ,= ,-_-. =.
bss@iguanasuicide.net ((_/)o o(\_))
ICQ: 514984 YM/AIM: DaTwinkDaddy `-'(. .)`-'
http://iguanasuicide.net/ \_/
 
Old 01-14-2009, 06:32 AM
Ron Johnson
 
Default Question about LVM and volume images on loop

On 01/13/09 23:18, Paul E Condon wrote:
[snip]


Yes, it's not hardware. Truth is it's vfat. I have had difficulty with
Western Digital USB HD when I try to reformat tham for ext3, and they
special software from WD to rewrite the vfat format.


?????

Doesn't Debian see it as an sd device? What errors do you get when
you mke2fs the device?



A software overlay
seemed a good way to go. I'm still hoping.


Just too overcomplicated.

Sell that device to a Windows-using friend, and for $120 buy a cheap
enclosure + OEM 1TBB hdd.)


--
Ron Johnson, Jr.
Jefferson LA USA

"I am not surprised, for we live long and are celebrated poopers."


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Old 01-14-2009, 08:29 AM
Paul E Condon
 
Default Question about LVM and volume images on loop

On Wed, Jan 14, 2009 at 12:27:08AM -0600, Boyd Stephen Smith Jr. wrote:
> On Tuesday 13 January 2009, Paul E Condon <pec@mesanetworks.net> wrote
> about 'Re: Question about LVM and volume images on loop':
> >On Tue, Jan 13, 2009 at 08:33:46PM -0600, Boyd Stephen Smith Jr. wrote:
> >> On Tuesday 2009 January 13 19:36:22 Paul E Condon wrote:
> >> >I do this because I want to
> >> >store large files on a HD whose hardware interface
> >> >limits file sizes to 4Gb, and I want to store larger
> >> >files than 4Gb. ( The HD has 500Gb total capacity.)
> >>
> >> HD hardware interfaces do not know where files begin and end.[1] You
> >> *might* be using a filesystem that limits you to 4Gb. If so, LVM won't
> >> buy you anything and you'll have to switch filesystems.
> >
> >My hope is that I can write a bunch of 4G files mount them as 4G hard
> > drives, and group them into a single 'volume group' whose total capacity
> > is some large multiple of 4G. Is this impossible?
>
> It's probably a bad idea. BUT, it should be possible.
>
> It would be much better to use ext[234], jfs, xfs, or even reiserfs
> directly on the drive. You say you have problems, but I'm using reiserfs
> across a raid-0 on WD driver and reiserfs across a raid-1 on WD drives
> without issues. Could you go into more details.

I tried ext3 about a year ago and I could get it onto the disk. I couldn't
remember the details of why it didn't work, so I decided to try again to
gather some current data with which to confront this community, but ---
IT WORKED! Thanks to all for provoking me into new action!

--
Paul E Condon
pecondon@mesanetworks.net


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Old 01-14-2009, 01:24 PM
Brian McKee
 
Default Question about LVM and volume images on loop

On Tue, Jan 13, 2009 at 8:36 PM, Paul E Condon <pec@mesanetworks.net> wrote:
> I do this because I want to
> store large files on a HD whose hardware interface
> limits file sizes to 4Gb, and I want to store larger
> files than 4Gb. ( The HD has 500Gb total capacity.)

As the others have pointed out - that doesn't seem likely. A drive is
just a bit bucket that doesn't grok it's own contents.

However, let's say for the sake of argument you don't want to have any
files over 4 gig. Why not shrink the existing partition and create a
series of 4 gig partitions, then use them for physical volumes in LVM.
Much simpler than getting loop devices in there etc.

Brian


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