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Configuring your first SAN: Creating your LUNs

For a small to medium size company with 12 servers (no failover server), I want to create a mirror/snapshot of the system drive (OS + database + application server settings). The reason is that after a server and an OS go down, reinstallation of an OS +application server + database server takes twice as long (four hours) as restoring database from database backup files (two hours). How will a SAN help in this case? We have 14 (73 GB, 10K rpm) internal disks per server for a total of 164 disks. Is $150K a reasonable target for moving all the disks into a SAN with tape library support with currently having seven DAS tape drives -- one tape drive per two servers -- for a total of five TB data full backup in the weekend and 0.3 TB incremental every weeknight?

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Click here to go back to part one of this series Configuring your first SAN: Usable versus raw storage.

You'll also need a backup solution that supports shared SAN-based tape libraries, such as Veritas Backup Exec or NetBackup, Legato Networker or CA ARCserve. If you want to reuse your DAT drives, you can get a data router (like the one depicted in part one), to attach your SCSI tape drives to the Fibre Channel fabric. Maybe a library with a tape changer makes more sense, since you can then automate backup and no one needs to be around to change tapes! Once everything is hooked together, you need to create your LUNs in the SAN to match your current LUN structure on your servers. Your SAN LUN sizes should be the same, or larger, than you currently use. Be sure to create one LUN 0 for each server on the dedicated mirrors to act as your boot volumes. To migrate the data, once the HBAs are installed in your servers and you have LUNs assigned in the arrays that match your current LUNs, you have three choices:

  1. Do it yourself via backup/restore to the new SAN-based LUNs.
  2. Do it yourself by creating host-based mirrors for the data volumes, then break them once all the data is mirrored.
  3. Have your SAN vendor migrate your data for you.

If you feel uncomfortable doing it yourself, I would have your SAN vendor do it for you under a statement of work. To create a bootable image in the SAN for each server, you will need to enable the boot BIOS on your HBAs, and use the LUN 0 you created for each server to act as your boot volume. You then install the operating system normally on your SAN boot disks. Reinstall the applications and databases, or just restore the system disk from tape since all your data is already moved over. You can then safely remove your internal server storage. Click here for part three.

This was first published in June 2004

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