| The 12 Days of dd: Day Ten | | Print | |
| Written by Brian E. Dykstra | |||
| Saturday, 03 January 2009 00:00 | |||
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On the tenth day of dd, we dd a tape (part one of two). When it comes to using tapes, there is a lot more involved than just a few command line prompts. There is typically more prep work involved in making sure your tape drive is running properly. This is because most people don’t already have a tape drive up and running like the rest of the drives we have looked at. We will start by looking at our equipment setup before we get into the dd commands. The first thing you need to do is make sure that you've got a SCSI card with a 68-pin connector in your Linux system. I recommend using a solid Adaptec SCSI card like the AHA-2940. You really can't go wrong with Adaptec SCSI cards; there is driver support for Adaptec cards in almost every OS. I used Fedora Core 3 for all the duplication, you could probably also use a bootable CD-ROM like Knoppix but I like an installed OS for really long processes like this. Knoppix does have automatic detection and driver support for Adaptec SCSI controllers. Next you’re going to need a tape drive. I recommend checking The Linux Tape Device Certification Program web site before purchasing your tape drive. Tape drives are expensive and it's best to be sure that you are going to get hardware that someone else has actually had some luck with before dropping big bucks. I always check the certification list before purchasing a tape drive and I've never had a drive that wouldn't work. When it comes to getting a tape drive right away I recommend CDW, they aren't always the cheapest but when you need the equipment right and right away you can count on them. I've been using the same account manager at CDW at four different companies for the past ten years and they have never disappointed me. It's also nice to be able to call an account manager and find out critical information prior to making your purchase, such as, “Does a SCSI cable come included with this tape drive?” I've used Sony, Quantum, Overland and HP tape drives over the past 4-5 years and have found all but the HPs to be very reliable. I've experienced a number of drive failures and robot arm failures on HP systems. Once you have all the equipment together and connected it is time to get started. The first thing you should do is write-protect your source tape. There is no magic to write protecting the tape; it is usually just a slider on the back or side of the tape. The magic is in figuring out which way the slider has to be positioned to be write-protected. The only good way to figure this out if you don't have the instructions that are packaged with the tape is to go to the manufactures web site and dig the information up. Beware that write-protection on some tapes is not perfect you can still erase some tapes even when the write-protect is activated. SCSI tape devices on a Linux system are recognized as /dev/st0 and /dev/nst0. /dev/nst0 is the same tape device as /dev/st0 but the /dev/nst0 tells the tape drive not to automatically rewind the tape. For everything we do here we want to use /dev/nst0. Obviously if you have more than one tape drive attached they will be /dev/st0, /dev/st1 and so on. Be sure to check the dmesg if you are having problems (dmesg | less). Good dmesg output should look like this: SCSI subsystem initialized We’ll finish up dding a tape tomorrow, on the eleventh day. Click here to continue to part two.
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