July 10th, 2006
Are Tape Backup systems obsolete?
One of the most tedious and complex jobs in the world of IT is data backup. Not only is it complex, but the use of mechanical Tape loaders make the system very prone to breakage and the Tapes themselves are not very durable and must be discarded on an annual or at least on a biannual basis. Conventional IT wisdom has always dictated that Tape Backup is the only way to economically backup large amounts of data, but does this still hold true in the age of ultra-cheap hot-swappable Hard Drives?
Let’s take a state-of-the-art Tape backup system like the HP Storageworks 1/8 Ultrium 960 Autoloader. I chose this particular device because it represents one of the most cost effective Tape Backup solutions with very high performance and capacity at a relatively low price. Each Ultrium 960 Tape has a true capacity of 400 Gigabytes and the HP Autoloader is capable of housing 8 Tapes at a time with a read/write throughput of 80 megabytes per second. The lowest price I found for Ultrium 960 Tape was $68 per Tape and the HP Autoloader was $5000.
Now we look at what it would take to do the exact same thing using Serial ATA hot-swappable Hard Drives. 400 GB SATA Hard Drives cost $142 and it would probably cost an extra $800 for a server that could house all the extra drives internally compared to something that would act as the server for the Tape Backup Autoloader. We won’t count the SATA controllers because the Tape Backup system would need a fast SCSI controller anyways so it would be a wash in this respect.
If we tried to build two 8 by 400 GB backup sets which is 6.4 terabytes, the Tape Backup solution would come out to $6088 and the SATA Hard Drive based solution would be $2272. If we didn’t actually need that big a backup set, the Hard Drive based solution would be even more economical since the $5000 Autoloader isn’t needed. In order for the Tape Backup system to become more economical, I calculated that it would require more than 56 Tapes to break even. That would be a massive 28 by 400 GB backup set which is massive even for large enterprises. Furthermore, Hard Drives are rapidly dropping in price and 300 GB Hard Drives are already in the sub $100 range. The other factor that comes in to play is that Hard Drives last 2 to 4 times longer because Tapes are suppose to be rotated ever year while most larger hard drives have a 5 year warrantee so it can be argued that even the media itself is cheaper since you don’t have to replace them as often.
Furthermore, Hard Drive based solutions are MUCH faster than any Tape Backup solution. Having 8 SATA Hard Drives can operate at the same time and have an aggregate throughput of about five times faster than a single Ultrium 960 Tape. While an Autoloader can hold 8 Tapes, only one Tape can be read or written to at a time. Autoloaders are also mechanically complex and they break down often and they’re very difficult to manage. Note that in order to fully saturate the capacity of 8 Hard Drives, you must have a 10 Gigabit Ethernet adapter on the server. Fortunately the cost of these adapters have come down to around $1000 but you’ll still need a 10 Gigabit capable switch to plug it in to.
The other HUGE factor is the fact that you don’t need to "rewind" a Hard Drive since it is random access. This actually permits the use of bit-level backup solutions that let you maintain a synchronized copy of a file system without copying the entire file. Windows Server 2003 for example would also allow you to implement a single-point storage system where replicas of files are only stored once on a file system. The combination of all these factors can increase backup and restore performance several times.
Most modern backup software will permit the use of Hard Drive based solutions. Off-site storage services don’t care if you hand them a container with a Tape or a Hard Drive. The only issue with Hard Drives is that you must put them in a thick-padded shock absorbent container but with proper care they should last much longer than Tapes [Update: Reader Adunlap posted this link where to get the padded casing]. So are the days of the Tape out numbered? Only time will tell and it takes a long time to change conventional wisdom.
George Ou is Technical Director of ZDNet. See his full profile and disclosure of his industry affiliations.
