Hard Drive Considerations

The main selling factor of any NAS is its storage capability. Currently, anything less than 1TB is rare, which is fortunate since many older IDE drives had a limit of 137.4GB because of the 28-bit addressing mode of Logical Block Addressing (LBA). Avoid anything smaller than 137.4GB in case the manufacturer is using old hardware under the hood, even if it supports an external USB drive, since that will invariably be governed by the same limitation.

Alongside the argument for disk space is the concept of disk format. This is usually given as FAT, FAT32, NTFS, or ext2 and limits the maximum file size possible (as shown in Table 3-1). The format also governs your likelihood of being able to recover it if you need to mount the drive in another machine.

Table 3-1. Filesystem Functionality

Filesystem

Maximum File Size

Maximum Volume Size

FAT 16

2GB

2GB

FAT32

4GB

2TiB or 8TiB*

NTFS

16EiB

16EiB

ext2/ext3

16GB to 2TiB

2TiB to 32TiB*

ZFS

16EiB

16EiB

* Variation depends on cluster size when formatted.

* Variation depends on cluster size when formatted.

So clearly, if you're wanting a NAS to store DVD images, you will need a filesystem that can support 4.7GB files. This usually means FAT-based systems are inadequate or that you will have to remove the DVD menus and reencode the movies into an alternative (and smaller) format.

The recover question is slightly more involved. If you ever have to remove the hard disk from its NAS mounting and place it in a standard PC to recover the data, you will need a PC that is able to read whatever filesystem is used by the NAS.

NTFS fairs slightly better in the Linux compatibility stakes, but not much. Although it's possible to read NTFS partitions under Linux, writing back to them is considered dangerous, although there are two open source drivers (Captive NTFS and NTFS-3G) that do support it. Additionally, there is a commercial driver (NTFS for Linux, from Paragon) that solves the same problem. For basic recovery, a read-only disc is fine, although you won't be able to repair the disk without reformatting it for the most part.

The natural solution is to use ext2 for any and all NAS drives, because this has the widest support in the Linux world. Many NAS devices now support this, so it can be worth spending a little more to get one because it ticks all the boxes. If your main desktop machine at home is Windows, then there are even ext2 recovery tools for Windows such as Linux Recovery from DiskInternals.

The type of data you're storing will determine the type of backup plan you need. When this is personal data, such as letters or photographs, then consider a NAS featuring built-in RAID functionality. These often autoconfigure themselves when a second drive is plugged in, so be warned if you insert a used drive thinking you'll gain extra space! Several types of RAID configuration are available, but the most common in this case is RAID-1, which uses a second drive to make identical copies of anything written to the first. It does this automatically and transparently from the user, so should either drive fail, the other can be used to recover the data. You should always remember, however, that RAID isn't a backup! It just makes it a bit less likely that you'll lose data to disk failure. It won't protect against corruption from controller failures, fire, flood, or theft.

■ Note Using hardware RAID solutions is a double-edged sword for some system administrators. They work seamlessly and take no effort to set up and maintain. However, if the RAID system has a problem and uses a custom disk format, then it might be impossible to recover the data on the disk. You can solve this by buying two pieces of hardware and verifying that you can swap the disks without a problem before they are put into active service. Alternatively, you can check with the manufacturer that the disk format used either is known or comes with suitable software recovery tools.

Backing up data, such as DVD or music rips, doesn't (and shouldn't) require RAID—although having one does no harm. Since this type of data changes less frequently, you can make do with an external USB hard drive plugged into your desktop machine. You can then run the backup software of your choice (see Chapter 6 for some possibilities here) to copy only those files that have changed and then unplug and store the drive. This prolongs the life of the drive and is worthy of the extra effort.

As with all backups, they are useless unless tested regularly, so make sure that you do test them. Some people will test them by copying their backups to a new drive every 6 to 12 months. The cost is negligible, compared to the many hours spent ripping and organizing the data. Furthermore, the price per gigabyte comes down every year, allowing you store more data in a smaller form factor. If you are desperate for extra space, you can then reuse the older drive elsewhere in your system. Although tape backup systems are a favorite of most businesses, the cost and convenience of USB hard drives render them unnecessary for the home market.

■ Note Hard drives either fail in the first few weeks or the day before you remember to back up. Therefore, when buying disks, always buy from different manufacturers and at different times, so if you get one disk from a bad batch (IBM Death Star, hang your head!), you minimize your chances of getting two.

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