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Author Topic: /home spanning 3hds?  (Read 2703 times)
franklin1k
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« on: October 02, 2008, 08:25:06 am »

/home spanning 3hds

If I use multiple hard drives, will my /home move on to the 2nd hd once the first one fills?

Or

Do I need to link the home directory with a symlink?

soho 5.9 deluxe
« Last Edit: October 03, 2008, 04:03:06 pm by franklin1k » Logged
newt
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« Reply #1 on: October 02, 2008, 08:30:34 am »

It may require setting those drives up in a RAID (software-RAID) so their seen and act as a single drive.  The biggest concern is if one of the drive goes bad I think you're screwed.  However, I've never done this sort of thing or looked into it very much.  It'll be interesting what you end up doing for the final solution.

Good luck!!
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Joe1962
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« Reply #2 on: October 02, 2008, 09:04:47 am »

RAID is one option, another is LVM (Logical Volume Management). LVM can also work over RAID. The problem is mostly one of choosing capacity or security, though most RAID versions can survive a single drive failure (except pure RAID 0, which is designed solely for speed and capacity). With 3 HDDs I think you can use RAID 5 (or 3 and 4, but those seem uncommon) and get the capacity of 2 disks plus one-drive-failure safety. Again, LVM is probably a good idea over RAID, as you can add drives (or arrays) later and dynamically extend volumes.

NOTE: Most of the above is "hearsay" ("readsay"?), as I have only ever used a RAID 0 setup... Wink

Links:
http://en.wikipedia.org/wiki/Logical_Volume_Manager_(Linux)
http://en.wikipedia.org/wiki/RAID
http://en.wikipedia.org/wiki/Standard_RAID_levels
http://www.gagme.com/greg/linux/raid-lvm.php
http://www.oreillynet.com/sysadmin/blog/2008/04/lvm_and_software_raid_a_powerf.html
http://aplawrence.com/Linux/lvm.html


« Last Edit: October 02, 2008, 09:08:59 am by Joe1962 » Logged

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The Headacher
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« Reply #3 on: October 02, 2008, 09:11:53 am »

If I were you, I'd just put some of the bigger subdirs on another drive and make symlinks to these in your home directory if possible. Especially those files you may want to use in other OS's as well, like music or video files. Very easy to do.
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franklin1k
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« Reply #4 on: October 02, 2008, 09:40:08 am »

Yes, putting all in just the /home seems good for somethings, but trouble with losing data when the structure breaks.

That leaves using the two extra drives for file storage.  Put all my music/audio books on one and video on the other, leaving the first hd for OS, apps and personal data.  My problem relates to too many years with Windows.  The Linux file system differs by not corresponding to physical location, like XP.  How do I tell linux to save files to their hd?

I have run across the concept of symbolic linking.  Being a noob perhaps means it might be twisted. 

ln -s /mnt/hdb /home/frank/video
ln -s /mnt/hdc /home/frank/music
ln -s /mnt/hdc /home/frank/audbook

Is this what I need to place the data on their drives?
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franklin1k
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« Reply #5 on: October 02, 2008, 09:48:16 am »

LVM, hmmrrr?  Let me read up a bit before speaking.

As for RAID, my understanding is the hds have to match.  Mine are 250 gb, 80 gb, and 60gb. 

more coffee and eyedrops
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bigpaws
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« Reply #6 on: October 02, 2008, 09:49:17 am »

Quote
The Linux file system differs by not corresponding to physical location, like XP

Actually it does just not the same way. If you mount a drive at a certain location the
only real difference is the name. So say you mount /dev/hdd /newdrive as you can see
anything that is placed in /newdrive will be on /dev/hdd.

Now the magic section you are looking for is fstab, which is located
at /etc/fstab this file tells the system where the mount points are.

So you can use the one drive as the drive for the root system. Then
add for example /dev/hdd and mount it on /music. So the process would
be to:

A.  As root (make the  directory) mkdir /music
B.  As root mount the dir: mount /dev/hdd /music
C.  As root add an entry in fstab so that the directory auto mounts.

You can follow from there.

You can also use VASM to do this under a GUI.

Now when a reinstall happens just do another mount
without formatting no loss of settings or information.

HTH

Bigpaws
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franklin1k
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« Reply #7 on: October 02, 2008, 05:48:12 pm »

Bigpaws

That clicks.  hd = folder /newdrive
Where would I find /newdrive when looking in the file system?  I know it can be found under "storage devices".  Starting from the /, is it in dev or mnt?  Is not /newdrive treated as a folder, or. have I missed the train?
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newt
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« Reply #8 on: October 02, 2008, 08:36:39 pm »

/newdrive is found under root (i.e. /), as indicated in the path.  And, yes, /newdrive is treated as a directory.

For example, /mnt/newdrive is found under /mnt
Another, /media/newdrive is found under /media

If you need help with bigpaws #C then give a shout.

Cheers!
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bigpaws
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« Reply #9 on: October 02, 2008, 08:41:29 pm »

You will not find it per se since the drive needs
to be registered (mounted) in order to be used.

Now the way to find a new drive is look at dmesg
in there you will find mention of /dev/xxx. Now look
in /etc/fstab and check against that so /dev/hda will
be listed in fstab, where say /dev/hdd may not be listed
in fstab.

The question about how it is treated. The boot sequence
uses a run time routine to find all devices. During an install
is when you register (mount) a drive. Until the drive is
setup and registered it is unusable. Then the directory is seen
but only by the label you gave it.

This may help with a better explaination:

http://www.tuxfiles.org/linuxhelp/mounting.html

The examples I used were to hopefully clearify how disks
work in Linux.

Bigpaws
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caitlyn
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« Reply #10 on: October 02, 2008, 09:18:43 pm »

Since the drives are of different sizes I would use LVM to create a single virtual volume spanning the three physical volumes (your three hard drives).  You're right about RAID -- just use JBOD (just a bunch of disks) and backup frequently in case of hard drive failure.  LVM isn't hard to use and once it's configured your three drives (or parts of them if you partition accordingly) will be treated like one big drive.  That's way easier than symlinks.
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franklin1k
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« Reply #11 on: October 05, 2008, 08:32:15 pm »

Thanks for your help.  I read up on LVM this weekend, and the Linux file system.  Bigpaw's A, B, C  is the way to go for now.  I need to familiarize myself with the nuts and bolts before moving on to other concepts.  Also, my needs of this box is static to a certain degree.

There is always another system to build another day.
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