Aug 01 Review
Volume Number: 17 (2001)
Issue Number: 08
Column Tag: Review
by Ben Baumer
Ecrix VXA Tape Drive
After having suffered through several years and many pounds of DLT III tapes on our old APS DLT III 2000 XT backup tape drive, we recently made the switch to Ecrix's new VXA tape drive, which uses revolutionary tape technology to produce extremely reliable backups on pint-sized tapes. So far, we've been pleased with the performance of the Ecrix drive, but in order to capitalize on the VXA's state-of-the-art technology, you will need some significant hardware that you may not be willing to allocate to a backup server.
There are three main advantages that the Ecrix VXA drive claims over your standard DLT or DAT drive: speed, reliability, and cost. As we all know, FireWire offers data transfer rates at up to 400 Mpbs, which can be twice as fast as your old SCSI interface. Although this sounds like a great savings, the likelihood of your backup server to achieve these speeds in practice is questionable. If you are backing up clients over a network, your maximum data transfer rate is already limited by the speed of the network (most likely 10 or 100 Mpbs), making the speed advantage of FireWire over SCSI inconsequential. It really doesn't matter how fast your computer can write to the tape if it's slower than the speed at which the computer can get the data from the client. For local backups, however, FireWire makes all the difference, and backup times will drop significantly. All of this assumes, of course, that you have a FireWire capable machine available as a backup server. We use a PowerMac 8500 with a G3 card and a PCI FireWire card. Substituting the Ecrix drive for our old SCSI DLT drive did not result in faster backups over the network. On local backups, however, I was able to achieve a top speed of a whopping 360 MB/min.!
Figure 1. Backup Speeds for the DLT SCSI Drive
|APS DLT 2000XT (SCSI) ||Local (MB/min.) ||Remote (MB/min.)
|Sustainable Speed ||100 ||50
|Maximum Speed ||120 ||55
Figure 2. Backup Speeds for the VXA FireWire Drive
|Ecrix VXA (FireWire) ||Local (MB/min.) ||Remote (MB/min.)
|Sustainable Speed ||250 ||50
|Maximum Speed ||360 ||55
As the tables above show quite clearly, Retrospect can write up to three times as fast to the VXA FireWire drive as it can to the DLT SCSI drive. However, on network backups, there is no discernible difference in speed between the two drives. Clearly, the network is the bottleneck in this example, and the superior performance of the VXA drive is lost. We have about 35 client machines in our backup cycle, and all but one (the backup server itself) are accessed over a network. For us, the gains of the VXA drive pale in comparison to gains we could make by upgrading our network speed. Since the whole idea of a backup server implies reliance upon a network, most people interested in the VXA drive will probably have a similar experience. While the drive itself functions brilliantly, it will probably not significantly improve the speed of your backup cycle if you are primarily backing up over a network.
As for reliability, I did not take the opportunity to dip my VXA tapes in a pot of coffee or hose them down. Personally, I have never had a problem with backup tapes deteriorating, but even the threat is disheartening. The VXA drive uses a new technology involving packets that Ecrix claims will greatly decrease the likelihood of losing data on a backup tape. Just as network traffic moves in packet form, the VXA drive writes only packets to the tape. Combine this with an interpolation algorithm, and VXA suddenly become remarkably reliable, since large chunks of the tape must be missing in order to make the tape unreadable. For a nifty demonstration of this technology, see http://www.ecrix.com/vxa/.
The diminutive physical size of the VXA tapes (roughly the size of audio cassette tapes) is a big plus if storage space is even a small concern, as backup sets tend to build up fast. Although the tapes are relatively expensive ($79.95 for the 33/66 GB V17 tapes), their price per gigabyte (~$1.21) is slightly less than that of the DLT tapes that we were buying ($38 for 15/30 GB tapes, ~$1.27/GB). However, with hardware compression on, I was only able to squeeze a maximum of 52 GB onto one of the VXA tapes, and an average closer to 45 GB. Comparatively, the DLT tapes averaged about 25 GB per tape, with a high of 28.5 GB. This makes both the effective average price per GB ($1.78, $1.52) and the effective maximum storage price per GB ($1.54, $1.33) swing in favor of the DLT tapes! While the price of DLT 15/30 tapes has been rising and will likely continue to do so, it is noteworthy that they come in under the VXA tapes in effective price per gigabyte. Also, Ecrix does offer two other tape types that all work with the VXA drive — the V10 (20/40 GB for $44.95) and the V6 (12/24 GB for $29.95).
While the Ecrix VXA FireWire tape drive is clearly a superior product, it is not necessarily the solution to your backup woes. If you rely heavily on network backups, the VXA drive will likely not make much of any improvement in backup time over your existing tape drive. However, if you concentrate your backups on local disks, then the speed of the FireWire VXA drive will slice your backup times in half or even in thirds. On the basis of price, there is no significant advantage to the VXA tapes over the DLT tapes (although that may change as outside vendors begin cloning and selling these VXA tapes). As for reliability, I cannot confirm or deny the ambitious claims of Ecrix, but after having used the drive for a few months, I have no reason to doubt these claims. I have no doubt that this drive will provide a fantastic solution in the right environment.