Wednesday, July 16, 2008

Terabyte experiments

The Station recently acquired an Iomega "StorCenter Network Hard Drive", which is an NAS (Network Attached Storage) device that comes in a sleek Iomega-ish dark green case. Inside are two 500 GB hard drives that can run as a single 1 TB drive in JBOD mode (look it up!) or in RAID 0 mode (look it up too!). Because I intend to use it for backup, reliability is important, so I will probably run it as a 500 GB RAID 1 device, where the two drives mirror each other.

The Iomega device is reviewed here. Unfortunately, the review does not focus on the NFS protocol supported by the device. That is important for me, because we are running Linux primarily.

As it turns out, while the Iomega NAS runs Linux internally, it does not provide fully Linux-friendly NFS export. User and group IDs and protection modes do not behave as they should, as I would have it. However, it does provide an amazing amount of functionality for 2.8 cents/MB.

If the NFS personality proves too troublesome, we can always remove the drives and put them in a new Linux box and run NAS any way we want.

Technical stuff: The problem with NFS on this box is that there is basically no security at all. You don't need much in a captive NAS server, but you would like to preserve owner, group, and protection data, at minimum. However, little of the usual metadata is stored with the files. No UID/GID identification or time of last update. So 'rsync' won't work properly as a mirroring tool unless you specify --size-only, which means that your mirror may not be exact. (E.g., if an updated file has the same size as the previous one.)

If you want to use this box for 'exact' Linux disk backup, you need to use an old-fashioned method like dump or tar, treating this server as a glorified tape drive. (But remember, it's cheap and tiny!)

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