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Can I expand file system without making any changes to paths ?

Posted on 2004-10-19
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Last Modified: 2010-04-20
Hi gurus


I like to buy one front server and one file server (NAS). I know that I can mount to NAS server usign TCP/IP connection. Let's say that on my front server is a folder /home  which actually points to NAS1 server. This works fine as we all know. But after running out of space on NAS1 I buy a new NAS server; NAS2.

Now to the problem: Is there a way to add server NAS2 to frontservers /home -path so that users doun't know are they using NAS1 or NAS2 server. And after running out off sapce on NAS2 I buy 3thr NAS server ...  So the key question is how to add space to a mount point without remaking a mount point ?

Thanks
Jussi
 
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Question by:salmjuh
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by:theruck
ID: 12345960
this is called distributed filesystem on windows
i have no idea if it is available on linux too so maybe try to google it
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TRobertson earned 32 total points
ID: 12346186
At that point you would have to mount additional shares under /home.
Ie. /home/nas1, /home/nas2, /home/nas3 or /home/a-i, /home/j-q, /home/r-z or something
If you needed more space you would have to add more drives to the NAS servers and extend the partitions.
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by:salmjuh
ID: 12346262
This is excally what I don't want to do. The point is that there is only one mount point /home which expands as need.

-jussi
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by:jlevie
ID: 12346665
Depending on how the NAS implements NFS you might be able to do this using an automounter. Doing so would require the NAS to treat a sub-dir of the NFS volume as exported and mountable. That is standard NFS behaviour and probably would be the case. Then you'd create an auto home map for each user. Initially all entires would point to the first NAS and as you add other units some of the entries would point to other unit.

A word of caution. Check the spec for the NAS very carefully and make sure that it will honor case sensitive names. I've seen several meant to be used with windows that don't and that creates a real problem for a Unix/Linux system.
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by:salmjuh
ID: 12346830
Ok, maybe I didn't write clearly what I want. And I think that /home -mountpoint was bad idea because it's givin a hint that I would like to use this to peoples home directory.

But the real purpose to one big folder is videos. As we all know video takes a LOT space. So I would like to have only ONE folder (exsample /VIDEOS) and not a single folder inside it. So all the videos are directly on the /VIDEOS folder.

And why only ONE folder ? Because I'm  writing a program which puts videos and delete those if needed. If there is multiple folders (=multiple NAS servers) as individual places it would be very difficut to handel space every servers. By grouping every NAS server as one "virtual" folder I can use exact all the space on every server without manually taking care where is free space and which server is full. I need space 4 TB per a year so thats why I need to do it this way.

Thanks advance
-Jussi

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by:Caseybea
Caseybea earned 31 total points
ID: 12347391
You *can* do what you want----   BUT, not this time.   What you really want to take advatnage of is "LVM" - Logical Volume Manager, but that's only available (by default) in the latest distribution(s) of RedHat EL. (Version 3, I believe).      

With Logical Volume Manager, you can expand file systems and even use parts of OTHER disks.

Unfortunately, since you didn't use LVM from the start; you have to start over (i.e., re-create the volume......).

Without LVM, and given the limitations you've described, you can't do what you want......

See THIS for info:   http://sources.redhat.com/lvm2/

And THIS for even more info:   http://www.tldp.org/HOWTO/LVM-HOWTO/

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by:de2Zotjes
de2Zotjes earned 31 total points
ID: 12347421
I can think of a way this might be done. You can use the net block device driver of the linux kernel combined with lvm and reiserfs can make a completely transparant solution. I don't have a clue what the performance would be like though.

Expanding a bit on what you would need to do:
assuming the nas systems are actually linux boxes with fast drives... you can run the net block service as a userspace daemon, making partitions available through the network.

You would create a volumegroup that holds the network-block devices (/dev/nd0...ndn). Using reiserfs you can expand the filesystem while it is online.

Biggest problem that I would foresee with this kind of setup is the reliability of the entire system, one disk failing is enough to kill the entire volume-group and thus munching all your data...
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by:de2Zotjes
ID: 12347458
Or wait.. you could stick RAID underneath by implementing that on all the nas boxes. Wouldn't be to simple to set up or maintain, but at least the reliability no longer rests on single disks. :-)
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by:jlevie
jlevie earned 31 total points
ID: 12348845
LVM, at least in its current state, isn't going to help with NAS devices since it is only usable for directly attached storage, like disks or SAN devices.

I really don't think that you want to have a single directory if you are contemplating something on the order of terabytes of storage. There's a performance penalty associated with large directories and there's a real risk that the number of files in that single directory will exceed the max inodes per directory. What I'd do is to use a hashing scheme to break up the repository into a directory hierarchy. Once you've done that automounting from multiple NAS units will work.
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by:Caseybea
ID: 12351401
Whoops-   Correct, I missed that these were NAS devices!   LVM won't work.   Ugh.     I agree about automounting and split hierarchies...  messy, but do-able...

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by:de2Zotjes
ID: 12352331
LVM can work, provided you use the net block device drivers. Not really mainstream and more than a little adventureous, but it can be done...
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