Backups & SAN Storage

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Enterprises typically spend huge dollars on their storage solutions (which admittedly are excellent). But if you don’t have several hundred thousand dollars, what do you do? Run CentOS!

We are putting together our backup solution – we use Bacula to manage our backups which is an excellent network aware solution that seems rock solid for us. We needed to compile our own RPMs from the source, but this was a simple matter of running:

# rpmbuild --rebuild --define "build_centos5 1" --define "build_postgresql 1" \
                     --define 'build_gconsole 1'--define 'build_bat 1' \
                     bacula-<version>.src.rpm

which we then imported into our yum repository. The configuration for this was pretty complicated the first time we set it up, but with the excellent HOWTOs on the site was not too much pain. We then had to decide where to store all the data. Tape drives are expensive, and slow and was not something we really wanted to do if we didn’t have to, so we built our own SAN. A SAN (Storage Attached Network) is a device which looks like a normal disk device on the computer, but in fact sends all the data across the network to a storage device.

Building a SAN is as simple as installing correct package and configuring it up:

# yum install scsi-target-utils
# chkconfig tgtd on
# service tgtd start
# /usr/sbin/tgtadm --lld iscsi --op new  --mode target --tid 1 \
                   -T iqn.2009-01.example.com.san1:storage.backup
# /usr/sbin/tgtadm --lld iscsi --op new  --mode logicalunit --tid 1 --lun 1 \
                   -b /dev/VolGroup00/Backup
# /usr/sbin/tgtadm --lld iscsi --op bind --mode target --tid 1 -I ALL
# echo >> /etc/rc.local <<EOF
/usr/sbin/tgtadm --lld iscsi --op new  --mode target --tid 1 \
                 -T iqn.2009-01.example.com.san1:storage.backup
/usr/sbin/tgtadm --lld iscsi --op new  --mode logicalunit --tid 1 --lun 1 \
                 -b /dev/VolGroup00/Backup
/usr/sbin/tgtadm --lld iscsi --op bind --mode target --tid 1 -I ALL
EOF

and you are done. Then you need to bind to that storage on the server that requires access to it. This is as simple as:

# yum install iscsi-initiator-utils
# echo "InitiatorName=iqn.2008-11.example.com.`hostname`" \
  > /etc/iscsi/initiatorname.iscsi
# iscsiadm -m discovery -t st -p <san address>
# iscsiadm --mode node --targetname  iqn.2009-01.example.com.san1:storage.backup \
           --portal <san address>:3260 --login
# mount /dev/<new device> /mnt

You now have a working SAN hooked up to the machine that requires it. Couple this with drbd and you have a highly available storage setup which will run as fast as your network (Gig-E is obviously recommended for this). Using a distributed filesystem (such as GFS2) should allow many machines to access the same data simultaneously. However, we have not done this as yet.

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