f



mount on the same mount point

Hello,

I'm trying to mount 2 md devices (/dev/md4 and /dev/md5) on the same 
mount point. I have just read that it is possible.

Note : MD devices are JFS.

But, altough I get no error, I do not get what I expected : the second 
mount command makes the first mount invisible.

So, my 2 questions are :

1) is it possible to mount 2 MD devices on the same mount point?
2) If yes, how?

Thanks
0
climb65 (4)
10/9/2009 10:49:47 AM
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climb65 wrote:

> Hello,
> 
> I'm trying to mount 2 md devices (/dev/md4 and /dev/md5) on the same 
> mount point. I have just read that it is possible.
> 
> Note : MD devices are JFS.
> 
> But, altough I get no error, I do not get what I expected : the second 
> mount command makes the first mount invisible.
> 
> So, my 2 questions are :
> 
> 1) is it possible to mount 2 MD devices on the same mount point?
> 2) If yes, how?

I don't think it's possible. You can probably get something similar to what 
you want by using one of the many union-fs like implementations.


0
pk (435)
10/9/2009 11:01:25 AM
climb65 wrote:
> Hello,
> 
> I'm trying to mount 2 md devices (/dev/md4 and /dev/md5) on the same 
> mount point. I have just read that it is possible.
> 
> Note : MD devices are JFS.
> 
> But, altough I get no error, I do not get what I expected : the second 
> mount command makes the first mount invisible.
> 
> So, my 2 questions are :
> 
> 1) is it possible to mount 2 MD devices on the same mount point?

yes, but the results are as above.

> 2) If yes, how?

As you did it.

If what you want is for two disks to apparently 'share' the same flat 
directory space, then symlinks are possibly your friend.


> 
> Thanks
0
tnp (2409)
10/9/2009 12:08:23 PM
climb65 <climb65@laposte.net> wrote:
> I'm trying to mount 2 md devices (/dev/md4 and /dev/md5) on the same 
> mount point. I have just read that it is possible.

Yes it's possible.


> But, altough I get no error, I do not get what I expected : the second 
> mount command makes the first mount invisible.

That's exactly what should happen.


> 1) is it possible to mount 2 MD devices on the same mount point?
> 2) If yes, how?

Yes it is, by doing what you're doing. But it sounds like your expectation
differs from reality, and it would help somewhat if you were to explain
what you were actually trying to achieve.

Chris
0
chris-usenet (1132)
10/9/2009 2:00:39 PM
On Fri, 09 Oct 2009 10:49:47 +0000, climb65 wrote:

> Hello,
> 
> I'm trying to mount 2 md devices (/dev/md4 and /dev/md5) on the same
> mount point. I have just read that it is possible.
> 
> Note : MD devices are JFS.
> 
> But, altough I get no error, I do not get what I expected : the second
> mount command makes the first mount invisible.
> 
> So, my 2 questions are :
> 
> 1) is it possible to mount 2 MD devices on the same mount point? 2) If
> yes, how?
> 
> Thanks

Let's think about this for a second. If you did as you wanted and you 
tried to access a particular file - suppose there was a file on each disk 
with the same name - how would the system know which one you wanted? If 
you created a file in the common directory - where would it be stored?
0
ray65 (5421)
10/9/2009 3:14:37 PM
On Oct 9, 11:14=A0am, ray <r...@zianet.com> wrote:
> On Fri, 09 Oct 2009 10:49:47 +0000, climb65 wrote:
> > Hello,
>
> > I'm trying to mount 2 md devices (/dev/md4 and /dev/md5) on the same
> > mount point. I have just read that it is possible.
>
> > Note : MD devices are JFS.
>
> > But, altough I get no error, I do not get what I expected : the second
> > mount command makes the first mount invisible.
>
> > So, my 2 questions are :
>
> > 1) is it possible to mount 2 MD devices on the same mount point? 2) If
> > yes, how?
>
> > Thanks
>
> Let's think about this for a second. If you did as you wanted and you
> tried to access a particular file - suppose there was a file on each disk
> with the same name - how would the system know which one you wanted? If
> you created a file in the common directory - where would it be stored?

What he wants is a "union mount".   See my http://aplawrence.com/Words/2004=
_11_21.html

--
Tony Lawrence
0
pcunix (620)
10/9/2009 4:09:14 PM
On Oct 9, 11:14=A0am, ray <r...@zianet.com> wrote:

> Let's think about this for a second. If you did as you wanted and you
> tried to access a particular file - suppose there was a file on each disk
> with the same name - how would the system know which one you wanted? If
> you created a file in the common directory - where would it be stored?

The ramifications of union mounts can be confusing.

The system doesn't know which one you wanted - but it does know which
one you'll get :-)

A more interesting question is what happens when a file in the upper
mount is deleted but a file with the name exists below.   Should the
"under" file become visible?  The answer depends upon whether or not
"whiteouts" are implemented.

See http://aplawrence.com/foo-mac/union-mounts.html for an example
(which happens to be on Mac OS X but the same concepts apply to Linux
union mounts).
0
pcunix (620)
10/9/2009 4:23:26 PM
On Fri, 9 Oct 2009, climb65 wrote:

> Hello,
>
> I'm trying to mount 2 md devices (/dev/md4 and /dev/md5) on the same
> mount point. I have just read that it is possible.
>
What exactly are you trying to do?

The minute you mount something to a mount point, whatever is there 
disappears until the mounted partition is unmounted (and then it
reappears unharmed).  A mount point is merely a directory, if it's empty
it means nothing to mount something there, if it's got content the content
disappears until there is a umount.

One can mount on a subdirectory of a mount point.

I have /home in a separate partition.  When I move to a new release of my 
distribution, I put it in a new partition, and play with it there for a 
while, in tandem with the previous release.  When I'm ready to make the 
changeover, I make /home in the new release's partition the mount point
for my separate /home partition.

But, I also have a directory in my /home directory titled "mnt", where I 
can mount flash drives and such.  So I have a mount point within a mounted
partition.

You can do that, mount one partition, create a directory where you can
mount the next, and once the first is mounted, you mount the second.
As someone pointed out, this also ensures that you can tell which 
content is in which partition, and if there are duplicates there won't
be a clash.

    Michael


> Note : MD devices are JFS.
>
> But, altough I get no error, I do not get what I expected : the second
> mount command makes the first mount invisible.
>
> So, my 2 questions are :
>
> 1) is it possible to mount 2 MD devices on the same mount point?
> 2) If yes, how?
>
> Thanks
>
0
et472 (516)
10/9/2009 5:04:09 PM
On Oct 9, 1:04=A0pm, Michael Black <et...@ncf.ca> wrote:
> On Fri, 9 Oct 2009, climb65 wrote:
> > Hello,
>
> > I'm trying to mount 2 md devices (/dev/md4 and /dev/md5) on the same
> > mount point. I have just read that it is possible.
>
> What exactly are you trying to do?

What he's trying to do is obviously a union mount.

Why does everybody keep insisting this can't be done?

http://www.filesystems.org/project-unionfs.html

0
pcunix (620)
10/9/2009 6:10:13 PM
On Fri, 09 Oct 2009 10:49:47 +0000, climb65 wrote:

> Hello,
> 
> I'm trying to mount 2 md devices (/dev/md4 and /dev/md5) on the same
> mount point. I have just read that it is possible.
> 
> Note : MD devices are JFS.
> 
> But, altough I get no error, I do not get what I expected : the second
> mount command makes the first mount invisible.

It worked correctly

> 
> So, my 2 questions are :
> 
> 1) is it possible to mount 2 MD devices on the same mount point? 2) If
> yes, how?
> 

No

-- 
GNU/Linux runs on IBM mainframes and on the world's fastest supercomputers
Windows supercomputers on the other hand are called botnets. <grin>
0
baho-utot3 (27)
10/9/2009 11:31:21 PM
On Fri, 09 Oct 2009 11:10:13 -0700, Tony  Lawrence (pcunix) wrote:

> On Oct 9, 1:04 pm, Michael Black <et...@ncf.ca> wrote:
>> On Fri, 9 Oct 2009, climb65 wrote:
>> > Hello,
>>
>> > I'm trying to mount 2 md devices (/dev/md4 and /dev/md5) on the same
>> > mount point. I have just read that it is possible.
>>
>> What exactly are you trying to do?
> 
> What he's trying to do is obviously a union mount.
> 
> Why does everybody keep insisting this can't be done?
> 
> http://www.filesystems.org/project-unionfs.html


What if unionfs is not available?

How would you make it work then?


-- 
GNU/Linux runs on IBM mainframes and on the world's fastest supercomputers
Windows supercomputers on the other hand are called botnets. <grin>
0
baho-utot3 (27)
10/9/2009 11:38:16 PM
Baho Utot <baho-utot@invalid.com> writes:

>On Fri, 09 Oct 2009 10:49:47 +0000, climb65 wrote:

>> Hello,
>> 
>> I'm trying to mount 2 md devices (/dev/md4 and /dev/md5) on the same
>> mount point. I have just read that it is possible.
>> 
>> Note : MD devices are JFS.
>> 
>> But, altough I get no error, I do not get what I expected : the second
>> mount command makes the first mount invisible.

>It worked correctly

On a regular mount, whatever is mounted on a mountpoint hides everything
that was previously on that mount point. The former stuff is
inaccessible. 

As people have pointed out there is a set of routines, called Union File
System, by which you can mount inclusively-- ie all the material mounted
as a union file system is accessible. 

Read http://en.wikipedia.org/wiki/UnionFS
Linux has both unionfs and aufs as implimentations.



>> 
>> So, my 2 questions are :
>> 
>> 1) is it possible to mount 2 MD devices on the same mount point? 2) If
>> yes, how?
>> 

>No

0
unruh-spam (2990)
10/10/2009 12:15:02 AM
Baho Utot <baho-utot@invalid.com> writes:

>On Fri, 09 Oct 2009 11:10:13 -0700, Tony  Lawrence (pcunix) wrote:

>> On Oct 9, 1:04 pm, Michael Black <et...@ncf.ca> wrote:
>>> On Fri, 9 Oct 2009, climb65 wrote:
>>> > Hello,
>>>
>>> > I'm trying to mount 2 md devices (/dev/md4 and /dev/md5) on the same
>>> > mount point. I have just read that it is possible.
>>>
>>> What exactly are you trying to do?
>> 
>> What he's trying to do is obviously a union mount.
>> 
>> Why does everybody keep insisting this can't be done?
>> 
>> http://www.filesystems.org/project-unionfs.html


>What if unionfs is not available?

>How would you make it work then?

You don't. 
Or you install unionfs or aufs and run the modules. 



0
unruh-spam (2990)
10/10/2009 12:16:13 AM
On Fri, 09 Oct 2009 11:10:13 -0700, Tony  Lawrence (pcunix) wrote :
(...)



Hello guys and thanks for your answers.

Yes, what I'm looking for is a cumulative mount, as you call it 
"unionfs".

For instance :

/dev/md4 and /dev/md5 will be moutned as /mnt/data.

In this mount point, I will have a global directory, say GD. On each md 
device, I have this GD directory.

Then, on one md device, I have for example, 3 directories, say DA, DB and 
DC. On the second md device, I have DD and DE.

my resulting mount point would be then as follows :

/mnt/data/GD/DA/
/mnt/data/GD/DB/
/mnt/data/GD/DC/
/mnt/data/GD/DD/
/mnt/data/GD/DE/

But as you said, my potential problem is that in D[A-E] directories, I 
have files with the same name. There is just the main directory (DA, DB, 
etc) which differs.

Is that a real problem?

Anyway, I've just learned something. I didn't know the existence of these 
2 modules :
- unionfs
- aufs

I will look them with attention.

Thanks

0
climb65 (4)
10/12/2009 10:20:16 AM
climb65 wrote:
> On Fri, 09 Oct 2009 11:10:13 -0700, Tony  Lawrence (pcunix) wrote :
> (...)
> 
> 
> 
> Hello guys and thanks for your answers.
> 
> Yes, what I'm looking for is a cumulative mount, as you call it 
> "unionfs".
> 
> For instance :
> 
> /dev/md4 and /dev/md5 will be moutned as /mnt/data.
> 
> In this mount point, I will have a global directory, say GD. On each md 
> device, I have this GD directory.
> 
> Then, on one md device, I have for example, 3 directories, say DA, DB and 
> DC. On the second md device, I have DD and DE.
> 
> my resulting mount point would be then as follows :
> 
> /mnt/data/GD/DA/
> /mnt/data/GD/DB/
> /mnt/data/GD/DC/
> /mnt/data/GD/DD/
> /mnt/data/GD/DE/
> 
> But as you said, my potential problem is that in D[A-E] directories, I 
> have files with the same name. There is just the main directory (DA, DB, 
> etc) which differs.
> 
> Is that a real problem?

Also look into LVM for concatenating volumes into one logical volume, RAID0.
0
joe248 (217)
10/12/2009 5:32:41 PM
Joe Beanfish <joe@nospam.duh> writes:

>climb65 wrote:
>> On Fri, 09 Oct 2009 11:10:13 -0700, Tony  Lawrence (pcunix) wrote :
>> (...)
>> 
>> 
>> 
>> Hello guys and thanks for your answers.
>> 
>> Yes, what I'm looking for is a cumulative mount, as you call it 
>> "unionfs".
>> 
>> For instance :
>> 
>> /dev/md4 and /dev/md5 will be moutned as /mnt/data.
>> 
>> In this mount point, I will have a global directory, say GD. On each md 
>> device, I have this GD directory.
>> 
>> Then, on one md device, I have for example, 3 directories, say DA, DB and 
>> DC. On the second md device, I have DD and DE.
>> 
>> my resulting mount point would be then as follows :
>> 
>> /mnt/data/GD/DA/
>> /mnt/data/GD/DB/
>> /mnt/data/GD/DC/
>> /mnt/data/GD/DD/
>> /mnt/data/GD/DE/
>> 
>> But as you said, my potential problem is that in D[A-E] directories, I 
>> have files with the same name. There is just the main directory (DA, DB, 
>> etc) which differs.

You give unionfs a list of priorities. Thus if you make /dev/md5 have priority,
then if there are files DA/file1 on both md4 and md5 it is the one on md5 that you
will see in the unionfs.

Note that having DA/file1 on md4 and DE/file1 on md5 is not a problem. They are
different -- are in diffeent directories. Just as you can have the same filename
in different directories on one filesystem.
I do not know what you call D[A-E] the "main directory" I assume you want to mount
both md4 and md5 onto /mnt/data/GD. That is the "main directory"



>> 
>> Is that a real problem?

No idea. Is it? You are the one who knows what he wants.


>Also look into LVM for concatenating volumes into one logical volume, RAID0.
0
unruh-spam (2990)
10/12/2009 6:56:58 PM
On Oct 9, 1:04 pm, Michael Black <et...@ncf.ca> wrote:
> What exactly are you trying to do?

"Tony  Lawrence (pcunix)" <pcunix@gmail.com> wrote:
> What he's trying to do is obviously a union mount.

If I didn't know better I'd say you hadn't been around for long(!) People
ask /really/ weird questions on usenet because they don't know how to
even approach a solution to their issue.

Chris
0
chris-usenet (1132)
10/12/2009 9:31:12 PM
Em Sexta 09 Outubro 2009 11:49, climb65 escreveu:

> Hello,
> 
> I'm trying to mount 2 md devices (/dev/md4 and /dev/md5) on the same
> mount point. I have just read that it is possible.
> 
> Note : MD devices are JFS.
> 
> But, altough I get no error, I do not get what I expected : the second
> mount command makes the first mount invisible.
> 
> So, my 2 questions are :
> 
> 1) is it possible to mount 2 MD devices on the same mount point?
> 2) If yes, how?
> 
> Thanks

can you read two cds on the same drive?

0
10/12/2009 10:15:27 PM
On Monday 12 October 2009 19:32 in comp.os.linux.misc, somebody
identifying as Joe Beanfish wrote...

> climb65 wrote:
>
>> Hello guys and thanks for your answers.
>> 
>> Yes, what I'm looking for is a cumulative mount, as you call it
>> "unionfs".
>> 
>> For instance :
>> 
>> /dev/md4 and /dev/md5 will be moutned as /mnt/data.
>> 
>> In this mount point, I will have a global directory, say GD. On each
>> md device, I have this GD directory.
>> 
>> Then, on one md device, I have for example, 3 directories, say DA, DB
>> and DC. On the second md device, I have DD and DE.
>> 
>> my resulting mount point would be then as follows :
>> 
>> /mnt/data/GD/DA/
>> /mnt/data/GD/DB/
>> /mnt/data/GD/DC/
>> /mnt/data/GD/DD/
>> /mnt/data/GD/DE/
>> 
>> But as you said, my potential problem is that in D[A-E] directories,
>> I have files with the same name. There is just the main directory
>> (DA, DB, etc) which differs.
>> 
>> Is that a real problem?

As long as you don't end up with identical filenames - case-specific -
in one and the same directory, that should not be a problem.

> Also look into LVM for concatenating volumes into one logical volume,
> RAID0.

Please note that the concatenation of separate volumes into one larger
volume is not the same thing as RAID 0.  RAID 0 is a single volume
which is striped across two or more physical disks, so that with two
disks, half of the data - if you have more disks in the stripe, it's
the total amount of data divided by the number of disks - is written to
one disk and the second half to the other disk.  

It is called RAID 0 because it doesn't offer redundancy.  If one disk in
the array fails, you won't be able to access your data anymore because
a chunk of it will be missing.  RAID 0 is typically deployed for
performance reasons, because it can be written to and read from faster
than when using a single disk.

That which you are referring to, i.e. the concatenation of separate
volumes into one larger volume, is not RAID but is typically referred
to as a "linear array".  If it is applied to more than one physical
disk, we generally speak of JBOD ("Just a Bunch Of Disks").

-- 
*Aragorn*
(registered GNU/Linux user #223157)
0
aragorn (581)
10/12/2009 11:49:43 PM
Aragorn <aragorn@chatfactory.invalid> writes:

>On Monday 12 October 2009 19:32 in comp.os.linux.misc, somebody
>identifying as Joe Beanfish wrote...

>> climb65 wrote:
>>
>>> Hello guys and thanks for your answers.
>>> 
>>> Yes, what I'm looking for is a cumulative mount, as you call it
>>> "unionfs".
>>> 
>>> For instance :
>>> 
>>> /dev/md4 and /dev/md5 will be moutned as /mnt/data.
>>> 
>>> In this mount point, I will have a global directory, say GD. On each
>>> md device, I have this GD directory.
>>> 
>>> Then, on one md device, I have for example, 3 directories, say DA, DB
>>> and DC. On the second md device, I have DD and DE.
>>> 
>>> my resulting mount point would be then as follows :
>>> 
>>> /mnt/data/GD/DA/
>>> /mnt/data/GD/DB/
>>> /mnt/data/GD/DC/
>>> /mnt/data/GD/DD/
>>> /mnt/data/GD/DE/
>>> 
>>> But as you said, my potential problem is that in D[A-E] directories,
>>> I have files with the same name. There is just the main directory
>>> (DA, DB, etc) which differs.
>>> 
>>> Is that a real problem?

>As long as you don't end up with identical filenames - case-specific -
>in one and the same directory, that should not be a problem.

Identical filenames are fine. Identical filenames and identical paths are the
problem. Ie, if on md4 you have
/DA/carlton.jpg
and on md5 you have /DA/carlton.jpg
then the priority is used to choose one of these to display.
(Not sure what happens if you union mount, and then you erase /DA/carlton.jpg
which erases the priority one, does the other one pop up to take its place?)



0
unruh-spam (2990)
10/13/2009 12:08:21 AM
On Tuesday 13 October 2009 02:08 in comp.os.linux.misc, somebody
identifying as Unruh wrote...

> Aragorn <aragorn@chatfactory.invalid> writes:
> 
>> On Monday 12 October 2009 19:32 in comp.os.linux.misc, somebody
>> identifying as Joe Beanfish wrote...
> 
>>> climb65 wrote:
>>>
>>>> Yes, what I'm looking for is a cumulative mount, as you call it
>>>> "unionfs".
>>>> 
>>>> For instance :
>>>> 
>>>> /dev/md4 and /dev/md5 will be moutned as /mnt/data.
>>>> 
>>>> In this mount point, I will have a global directory, say GD. On
>>>> each md device, I have this GD directory. Then, on one md device, I
>>>> have for example, 3 directories, say DA, DB and DC. On the second
>>>> md device, I have DD and DE. 
>>>> 
>>>> my resulting mount point would be then as follows :
>>>> 
>>>> /mnt/data/GD/DA/
>>>> /mnt/data/GD/DB/
>>>> /mnt/data/GD/DC/
>>>> /mnt/data/GD/DD/
>>>> /mnt/data/GD/DE/
>>>> 
>>>> But as you said, my potential problem is that in D[A-E]
>>>> directories, I have files with the same name. There is just the
>>>> main directory (DA, DB, etc) which differs.
>>>> 
>>>> Is that a real problem?
> 
>> As long as you don't end up with identical filenames -
>> case-specific - in one and the same directory, that should not be a
>> problem. 
> 
> Identical filenames are fine. Identical filenames and identical paths
> are the problem. Ie, if on md4 you have
> /DA/carlton.jpg
> and on md5 you have /DA/carlton.jpg
> then the priority is used to choose one of these to display.

As I understand it, the one displayed will be the one of the filesystem
listed first.  It will cover/hide the one(s) on the filesystem(s)
listed behind that in the union.

> (Not sure what happens if you union mount, and then you erase
> /DA/carlton.jpg which erases the priority one, does the other one pop
> up to take its place?)

Possibly, yes, but - again, as I understand it, from only briefly
looking into this thing myself - this is something that can be
specified at mount time.  There should be several mount options there
to the /unionfs/ itself.

A quick Google search leads me to this:

http://myhowtosandprojects.blogspot.com/2008/07/install-and-use-unionfs-merging.html

<blockquote>

        Writing to union

        Merging read-only directories is useful in many cases, but the 
        union itself remains read-only too, until a read-write branch 
        is added to it. In that case, all changes are stored in leftmost
        branch (using copy-up method, see below) and file deletions are 
        done by using one of the two methods available:

        * WHITEOUT mode, inserts a .wh (whiteout) file to mask out a real
          file

        * DELETE_ALL mode, tries to delete all instances of a file from 
          all branches

        WHITEOUT mode is used as default. Copy-up is a special method used
        to handle file modifications in union. A file from ro branch can't
        be modified, so it is copied to upper (left) read-write branch at 
        the time when the modification should begin. Then the modification 
        is possible and modified file remains in rw branch.

</blockquote>

-- 
*Aragorn*
(registered GNU/Linux user #223157)
0
aragorn (581)
10/13/2009 12:29:37 AM
On Oct 12, 8:08=A0pm, Unruh <unruh-s...@physics.ubc.ca> wrote:

>
> Identical filenames are fine. Identical filenames and identical paths are=
 the
> problem. Ie, if on md4 you have
> /DA/carlton.jpg
> and on md5 you have /DA/carlton.jpg
> then the priority is used to choose one of these to display.
> (Not sure what happens if you union mount, and then you erase /DA/carlton=
..jpg
> which erases the priority one, does the other one pop up to take its plac=
e?)

What happens depends on if "whiteouts" are implemented.

If I remember correctly,  the Mac OS X implementation shows the
"under" file, but you can't delete it after deleting the "upper",
while Linux won't show the "under" after that upper is deleted - Linux
unionfs implements "whiteouts", the OS X didn't (though it may now - I
haven't tested it recently).



0
pcunix (620)
10/13/2009 2:33:55 AM
On Mon, 12 Oct 2009 18:56:58 +0000, Unruh wrote :

> Joe Beanfish <joe@nospam.duh> writes:
> 
>>climb65 wrote:
>>> On Fri, 09 Oct 2009 11:10:13 -0700, Tony  Lawrence (pcunix) wrote :
>>> (...)
>>> 
>>> 
>>> 
>>> Hello guys and thanks for your answers.
>>> 
>>> Yes, what I'm looking for is a cumulative mount, as you call it
>>> "unionfs".
>>> 
>>> For instance :
>>> 
>>> /dev/md4 and /dev/md5 will be moutned as /mnt/data.
>>> 
>>> In this mount point, I will have a global directory, say GD. On each
>>> md device, I have this GD directory.
>>> 
>>> Then, on one md device, I have for example, 3 directories, say DA, DB
>>> and DC. On the second md device, I have DD and DE.
>>> 
>>> my resulting mount point would be then as follows :
>>> 
>>> /mnt/data/GD/DA/
>>> /mnt/data/GD/DB/
>>> /mnt/data/GD/DC/
>>> /mnt/data/GD/DD/
>>> /mnt/data/GD/DE/
>>> 
>>> But as you said, my potential problem is that in D[A-E] directories, I
>>> have files with the same name. There is just the main directory (DA,
>>> DB, etc) which differs.
> 
> You give unionfs a list of priorities. Thus if you make /dev/md5 have
> priority, then if there are files DA/file1 on both md4 and md5 it is the
> one on md5 that you will see in the unionfs.
> 
> Note that having DA/file1 on md4 and DE/file1 on md5 is not a problem.
> They are different -- are in diffeent directories. Just as you can have
> the same filename in different directories on one filesystem. I do not
> know what you call D[A-E] the "main directory" I assume you want to
> mount both md4 and md5 onto /mnt/data/GD. That is the "main directory"
> 
> 

That sounds good. My directory D(n) will always be on a unique device. 
So, a file DA/file1 will never be both on md4 and md5.

There is just the global directory GD that will be on both md4 and 
md5. But inside GD, I will have the D(n) directories, each of them in a 
unique device (either md4 or md5)

So, here is a schema of what I could get :
                       _
/mnt/data/GD/DA/file1   )
/mnt/data/GD/DB/file1   )-- on md4 (RAID 10)
/mnt/data/GD/DC/file1  _)
                       _
/mnt/data/GD/DD/file1   )__ on md5 (RAID 10)
/mnt/data/GD/DE/file1  _)


Is there any problem with the parent directory GD? I think no but advice 
is welcome.

Thx

0
climb65 (4)
10/13/2009 2:09:15 PM
On Tuesday 13 October 2009 16:09 in comp.os.linux.misc, somebody
identifying as climb65 wrote...

> [...] My directory D(n) will always be on a unique device.
> So, a file DA/file1 will never be both on md4 and md5.
> 
> There is just the global directory GD that will be on both md4 and
> md5. But inside GD, I will have the D(n) directories, each of them in
> a unique device (either md4 or md5)
> 
> So, here is a schema of what I could get :
>                        _
> /mnt/data/GD/DA/file1   )
> /mnt/data/GD/DB/file1   )-- on md4 (RAID 10)
> /mnt/data/GD/DC/file1  _)
>                        _
> /mnt/data/GD/DD/file1   )__ on md5 (RAID 10)
> /mnt/data/GD/DE/file1  _)
> 
> Is there any problem with the parent directory GD? I think no but
> advice is welcome.

With the intended layout as you have depicted it here, there should be
no problem whatsoever.  You should be able to use /unionfs/ to mount
both devices to */mnt/data/GD.* ;-)

-- 
*Aragorn*
(registered GNU/Linux user #223157)
0
aragorn (581)
10/13/2009 2:22:24 PM
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