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There have been a lot of removable disk formats offered, suitable for backup use, that haven't been able to survive in the marketplace against inexpensive optical formats, auxiliary use of hard disk drives, and now falling prices for solid-state flash memory formats. Such orphaned formats would include Syquest SparQ, IOmega Jaz, Castlewood Orb, LS120, and magneto-optical. I doubt the IOmega Zip formats would still be lingering if they hadn't gotten their foot in the door so early.
Flash media, or memory cards, are solid-state nonvolatile flash memory packaged in tiny proprietary removable formats, and were first introduced as "film" for digital cameras. Ordinary RAM memory is relatively cheap but volatile; flash memory costs more but is nonvolatile. Your PC's BIOS chip is flash memory.
The only reason PCs have both RAM and disk drives is because RAM memory is volatile:
As of second quarter 2008, 4.7GB DVD-RW or DVD+RW disks are available for less than 50¢ per disk in quantity; flash media are available in capacities up to 16GB and 32GB, and cost is down to $4-$20 per GB, with the average around $10/GB. This is still 100× DVD's 10¢ per GB, but in my opinion flash media are now cheap enough to be a viable choice for backup.
Your computer will need a flash media reader. Drive-bay and portable USB-connect card readers are available, and usually support multiple flash media formats. Drive-bay readers are probably preferable for a desktop PC, if the case design permits. Many new laptop and desktop PCs now come with some provision for memory cards, usually SD/MMC. I've had good luck with a multi-format external reader from Epraizer, that's about the size of a matchbox, and they have a smaller one with a swiveling cover for the USB connector that looks good.
External portable USB hubs usually have their ports crammed together tightly to minimize the size of the hub for portability, but USB devices are often wider next to the plug than many hubs will accomodate side-by-side. Some portable memory-card readers have their plug on a swivel, or with a built-in short "pigtail" cable; or Cyberguys has one-foot and 7½-inch USB cables that can be helpful with this issue.
| Format & acronym | First year | Comments | Related formats | |
|---|---|---|---|---|
| Secure Digital | SD | 1999 | Postage-stamp size, 24×32×2.1mm; max capacity 2GB. One rarely sees SD cards with capacity other than 2GB now, and they're quite cheap. | miniSD and microSD are compatible with SD slots with adapters. |
| Secure Digital High Capacity | SDHC | 2006 | Same form factor as SD, capacity to 32GB with escalating prices, faster transfers. Some older card readers support SD format but not SDHC. | miniSDHC, microSDHC. |
| MultiMediaCard | MMC | 1997 | Same size as SD but thinner, 24×32×1.4mm; connectors compatible with SD/SDHC, and MMC cards should work in an SD slot. Very few devices are now built with MMC-specific slots. | RS-MMC, MMCmobile, MMCplus, MMCmicro. |
| CompactFlash | CF | 1994 | Oldest and physically largest card format, 43×36mm. CF/MD are the only pin and socket formats; all others use sturdier sliding contacts. | Most flash memory CF cards are the 3.3mm thick CF I format, not the 5mm CF II, which is mostly used for MD. |
| MicroDrive | MD | 1999 | Not flash memory: 1-inch hard disk packaged to fit the 5mm thick CF II form factor. Don't ask me why. | |
| Memory Stick | MS | 1998 | Long and narrow, 21.5×50×2.8mm. Sponsored by Sony, now producing cameras and camcorders with SDHC slots, and their own line of SDHC memory cards.¹ | Memory Stick Pro fits MS socket; Memory Stick Pro Duo, Memory Stick Micro (M2) compatible with adapter. |
| xD Picture Card | xD | 2002 | Tiny, 25×20×1.78mm. Sponsored by Olympus and Fujifilm; both have phased out xD support in favor of SDHC. | xD-M, xD-H both fit xD socket. |
There seems to be a shakeout of flash memory formats happening, and I think Secure Digital and CompactFlash, and their related formats such as SDHC and MicroDrive, will eventually be the only survivors. microSD and microSDHC are the smallest available memory card formats (about the size of a fingernail) and are getting to be the standard for memory card slots in cell phones.
CompactFlash seems to be sticking around for various reasons, in spite of its age, relative bulk, and somewhat vulnerable pins.² It's the physically largest memory-card format, which is useful for things like MicroDrive and expensive early high-capacity offerings like 32/64GB. CF format is inherently IDE/ATA compatible, and thought to be more shock-resistant than other formats. Several CF+ revised formats and the future SATA-based CFast format offer higher speeds. Adapters to allow SDHC cards to be used in a CF II slot are available for under US$20; other CF-slot adapters are available including Ethernet, Bluetooth, modem, and WiFi.
If you're going to use flash media for backup, I'd say you have four practical hardware choices:
Flash media are a lot easier for backup purposes than CD/DVD optical formats. You can just copy or XCOPY to flash media, as if they were a hard disk; no special software is required as with optical. You may find the utility JFileSync useful; it's cross-platform because it's written in Java, and it syncronizes pairs of directories. If you don't want to write on the tiny labels on the cards, you can assign volume names as with disks (right-click and select Properties). These volume names will show up in Windows Explorer. This works with USB thumb drives and the card formats.
Flash media will wear out eventually. How Long Does a Flash Drive Last? describes a 2008 test in which a Sony USB flash drive was deliberately driven to write failure; it took 90 million writes, and the drive contents could still be read, if not written.
USB flash drives or UFDs are essentially the same as other solid-state flash media, except they have a USB rather than proprietary connection interface, and can therefore plug directly into any PC with USB ports. They're very popular and have been dropping in price: as of first quarter 2008, about $20 for 2GB, and 1GB to 8GB are typical capacities offered. Most recent PCs come with handy front-panel USB ports, including the ones at my local public library branches and Fedex Kinko's stores. If your older home PC only has USB ports in back, inexpensive drive-bay adapters are available, or you could just get a USB hub.
The Backup sets section of my main Backup page says "You have to have at least two sets of backup media." If you want to use either proprietary or USB flash media as your primary backup system, this principle still applies. On the other hand, if you have just one USB thumb drive, for example, there's nothing wrong with backing up or synchronizing your documents to it also, as long as you use two or more sets of something else periodically as a primary backup, such as CD-R/RW or DVD.
Recordable and rewriteable CD formats work with CD-RW drives, also known as "CD burners." There's CD-R, which is a write-once format, and the slightly more expensive CD-RW, which lets you erase and overwrite stuff, within limits. There are internal IDE and SATA and external USB drives for these formats. These 120mm standard CD formats in general have the same 700MB nominal capacity as a CD-ROM, making them of limited usefulness for global backup with modern multi-gigabyte hard disks.
Mass-produced read-only CD-ROM disks were used for software distribution for years before the recordable formats were available, of course. Some older CD-ROM drives are unable to read the CD-R/RW formats, and some can read CD-R but not CD-RW. There's a spec that says you are supposed to be able to rewrite a CD-RW disk 1,000 times, and some brands claim as much as 100,000; your mileage may vary.
There are also some oddball auxiliary optical formats for the same drives, including pocket-size 180MB 80mm mini-CD format, mostly seen in movies and TV. Business-card CD format is just the mini-CD format with clipped sides to fit anywhere a business card will, sometimes called "hockey rink style" after the shape. The recordable area is just the circle remaining within the clipped sides, hence the capacity of only 50MB. Older CD-ROM drives may not be compatible with these smaller formats.
There are also recordable DVD formats for PCs: DVD-R, DVD-RW, DVD+R, and DVD+RW. As with the CD formats, the "R" formats are write-once and the "RW" formats are rewriteable. The dash (-) and plus (+) formats are competing standards, but you don't have to worry about that as long as you get a DVD±RW drive, which can handle all four formats. Standard DVD disks have a nominal capacity of 4.7GB. There's also an 80mm 1.4GB mini-DVD format.*
Optical formats for backup are so cheap, you can simply continue accumulating backup sets on a series of disks. This can allow you to go back and refer to old versions of your data from weeks or months in the past, at any time.
Blank media prices for these optical formats run $20-$40 per 100, with CD-R at the low end (2nd quarter 2008).
Hard disk drives with capacity up to hundreds of gigabytes have gotten amazingly inexpensive. Either of these methods can use them to provide large amounts of portable mass storage, for backup purposes, for two-way transport of large amounts of data, or both. You can work on the exact same data set at work and at home, without worrying about Windows Briefcase or version control. Software can even be installed on and run from these external or removable hard disks.
There are external enclosures for hard disk drives, with a fast USB cable connection to the PC, or sometimes eSATA. There are some very small enclosures for 1.8-inch or 2½-inch notebook drives, that are easy to slip into a briefcase, especially when used with a compact retractable USB cable. You might want to avoid the 1.8-inch drives; they tend to be significantly slower than regular 2½-inch laptop drives. There are also larger external enclosures for full-size 3½-inch drives.
One obvious advantage of a cable-connect external enclosure is that it can be quickly connected to any PC with USB ports, not just yours.
Removable hard disk racks are a variation on the same idea. You have an outer rack which you mount in an open 5¼-inch drive bay, and an inner rack or "cassette" that slides in and out of it, inside which you mount your 3½-inch drive. They come in different styles with various features and made of different materials, at varying prices, of course. Usually the cassette has an eject handle and the rack has a security lock and drive access light. Some have a cooling fan. Usually you can order additional cassettes, so you can set up multiple drives for the same rack.
If you adopt a removable rack system, consider buying an extra rack-plus-cassette setup, to be held in reserve. Then if it becomes appropriate later to set up a second PC for high volume two-way data transfer, perhaps a work PC, all you'll need to add is a drive. Or you can swap two drives in one PC, perhaps to allow you to boot your choice of two operating systems.
There are now drive-bay and external USB-connect trayless SATA drive docks for both 2½ inch and 3½ inch format SATA hard drives (not IDE). You just slide the bare drive into the dock to access it.
IOmega Zip drives use removable disk cartridges. You can get them as USB or FireWire portable external drives, or as an internal drive that fits in a 3½-inch drive bay with ATAPI interface (CDROM-style IDE).
Zip drives were one of the first high-capacity disk formats available, and have been widely used at places like public libraries, copy shops, and service bureaus. (Of course most of those places can process data on a CD-R or USB flash drive just as easily.) IOmega introduced 250MB and 750MB Zip formats, in addition to the original 100MB. Zip disks are magnetic media on a plastic substrate similar to diskettes, except that the magnetic emulsion is higher quality to support the higher data density.
I consider the Zip-drive formats somewhat inadequate for backup purposes, compared to the multi-gigabyte hard disk sizes now in common use.
| Site | 1st year | Capacity | Installed client | Supported OSes |
|---|---|---|---|---|
| ADrive | 2007 | 50GB | Optional | Browser-based (all) |
| Box.net | 2005 | 1GB | None | Browser-based |
| DropBox | 2007 | 2GB | Required | Windows, Mac, Linux |
| Humyo | 2007 | 10GB | Optional | Browser-based |
| IDrive | 1997 | 2GB | Required | Windows and Mac |
| MyOtherDrive | 2005 | 2GB | Optional | Browser-based |
| SpiderOak | 2007 | 2GB | Required | Windows, Mac, Linux |
| Wuala | 2008 | 1GB | Required | Windows, Mac, Linux |
These sites can be used to park files online for other purposes besides backup, of course. There are similar services based on paid subscriptions; I'm just talking about sites with free plans here. See also comparison of online backup services on Wikipedia.
Windows, Mac, and Ubuntu Linux all have online storage services specific to each OS. Windows has Live Mesh and Live SkyDrive, Apple/Mac has the iDisk subscription service, part of MobileMe, and Ubuntu has Ubuntu One. It makes perfect sense in promotional terms, but I tend to prefer resources everybody can use.
Wuala is a little different: it's a distributed peer-to-peer service, sort of like bittorrent, in which you essentially trade unused storage on your own local drive for more storage online, beyond the 1GB starter. This system requires that your computer be online and accessible at least four hours per day. The required client is Java-based and runs on at least Windows, Mac, and Linux. Apparently when you store something online on Wuala, it gets split up into multiple segments and stored redundantly all over the system.
Internet backup may meet your needs, but it doesn't feel like a real backup to me, at least in a primary role. You don't really have control over the archive; your access is dependent on the uptime of the remote server and the networks. If you back up with a local drive on local media, you have positive control of everything. Backup is a serious thing for me; sorta kinda part-way isn't good enough.
Internet backup sites do have interesting advantages. Since the system can be used from anywhere you can connect to the Internet, and no actual hardware is involved, it has obvious advantages for "road warriors." Repairs of any problems with the server systems are of course up to them. A system with local-drive primary backups, that's also backed up over the Internet as a second line of defense, would certainly be more secure than with the local-drive backups only.
Negative points would include the lack of positive control of the archive, any reservations you might have about data security and server uptime, and ongoing subscription fees charged by some remote backup services.
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