Managing Disk Space with LVM
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Network Access of Files

A file server isn't much use if you can't get files off of it. There are many ways to serve files, but the most common and powerful is Network File System (NFS). NFS allows other *nix machines to mount the file shares for direct use. It's also pretty easy to set up on Linux.

First, make sure the file server has NFS enabled in the kernel (2.6.15 in this example):

File systems
 Network File Systems

 <*> NFS file system support
  [*]   Provide NFSv3 client support
  <*> NFS server support
  [*]   Provide NFSv3 server support

Rebuild and reinstall the kernel and then reboot the file server. If you'd like to avoid rebooting, build NFS as a module and then load it with modprobe nfsd.

Next, start the NFS service. Your Linux distro will have an init script to do this. For instance, on Gentoo, you'll see:

/etc/init.d/nfs start 
 * Starting portmap ...      [ ok ]
 * Mounting RPC pipefs ...   [ ok ]
 * Starting NFS statd ...    [ ok ]
 * Starting NFS daemon ...   [ ok ]
 * Starting NFS mountd ...   [ ok ]

You can double-check that NFS is running by querying portmapper with the command rpcinfo -p | grep nfs:

program  vers proto port  service
100003    2   udp   2049  nfs
100003    3   udp   2049  nfs
100003    2   tcp   2049  nfs
100003    3   tcp   2049  nfs

Next, you must specify which directories the NFS service should export. Add the following to /etc/exports:

/var/backup    192.168.0.0/24(rw,sync)
/var/media     192.168.0.0/24(rw,sync)
/var/share     192.168.0.0/24(rw,sync)

This lists the directories to share, the machines (or networks) to permit to mount the files, and a set of options to control how the sharing works. The options include rw to allow read-write mounts and sync to force synchronous behavior. sync prevents data corruption if the server reboots in the middle of a file write, but sacrifices the performance advantages that async would provide.

Next, export these file shares from the NFS service:

# exportfs -av
exporting 192.168.0.0/24:/var/backup
exporting 192.168.0.0/24:/var/media
exporting 192.168.0.0/24:/var/share

Now, mount these file shares on each machine that will use them. Assuming the file server is named fileserv, add the following lines to the client machines' /etc/fstab files:

# Device               mountpoint    fs-type   options    dump  fsckorder
fileserv:/var/backup   /var/backup   nfs       defaults   0     0
fileserv:/var/media    /var/media    nfs       defaults   0     0
fileserv:/var/share    /var/share    nfs       defaults   0     0

Finally, create the mountpoints and mount the new shares:

# mkdir /var/backup /var/media /var/share
# mount /var/backup /var/media /var/share

Now all the machines on your network have access to large, reliable, and expandable disk space!

Backup Strategies

As you rely more heavily on this new LVM-enabled disk space, you may have concerns about backing it up. Using RAID ensures against basic disk failures, but gives you no protection in the case of fire, theft, or accidental deletion of important files.

Traditionally, tape drives are used for backups of this class. This option is still viable and has several advantages, but it can be an expensive and slow solution for a system of this size. Fortunately, there other options using today's technology.

rsync is a powerful utility for copying files from one system to another, and it works well across the Internet. You could set up a backup system at a friend's house in a different city and arrange to periodically send backups there. This is easy to do with cronjob:

04 4 * * 4  rsync --delete -a /var/backup/ fileserv.myfriend.org:/backup/myself/backup \
    > /var/log/crontab.backup.log 2>&1

Another approach is to attach a pair of external RAID 1 hard drives to your file server using Firewire, USB, or eSATA. Add one drive to /dev/md0 and the other to /dev/md1. Once the mirroring is complete, remove the drives and store them in a safe place offsite. Re-mirror weekly or monthly, depending on your needs.

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