The Trails and Tribulations of Tape – A Cautionary Tale

For most of us, we have some data on some computers that we’d like to keep. For some it is critical. However, it can be a minefield, and finding a suitable strategy can be difficult.

Having spent a lot of time in the past moving precious data from one hard drive to another, and using fault tolerant RAID arrays to protect important data, I decided that it would be a good idea to invest in a long term and repeatable backup, and tape seems to be the accepted way to do this.

Since I don’t want to invest the life-savings in a state of the art tape drive, an older (but still very capable) model should do for what I need.

Hence I have bought an HP LTO5 Drive – 1.5TB per tape native, and up to 3TB compressed, which depends entirely on what you are backing up. Assume 1.5TB to be on the safe side.

The LTO6 and 7 drives hold more data per tape, but the tapes are proportionately more expensive too, so LTO5 seemed like a good compromise.

However, if you’re used to using NAS or external Hard Drive as backup, tape seems to be an altogether more complicated thing and fraught with troubles.

As I have an HP server, I decided to buy an HP drive as that should ensure it was compatible. There are good second hand offers on eBay, but I found a “new unboxed” one for a good price and bought that.

Problem 1: SAS Connections

If you’re used only to SATA (as I am), SAS is quite a new and complicated thing. I checked the specs for the server I was going to put the drive in, and it says that it has SAS connections, so that should be all right? Wrong! While there are SAS connections in the server, the are all used in the 4 non-hot-swap drive bays. Ok, says I – I’ll plug in one of the HDDs into the SATA port, and free up a SAS port. Brilliant – the HDDs are fine, and the tape drive lights up.

Does Linux recognise it? Of course it doesn’t – the hard drive controller in the (albeit entry level) HP server offers SAS connectors and says SAS on the specification (I did check before buying the drive), but is only capable of driving SATA hardware. Thanks HP!

A new SAS controller card and suitable cables (an extra £200 odd) and I’m in business – or so I thought.

Problem 2: Warranty Support for Updates

So I try a backup – looks good, and then an error…

Try again… looks good… error.

Reading about the errors I was getting on various forums, the advise seems to be to update the tape drive firmware.

However, just because the product is advertised as “new” by the seller – don’t expect HPE to give you up-to-date firmware to go with it – this is “enterprise” kit you have to pay for support if the item is out of warranty – and there is no way of finding out if it is in warranty if you don’t buy from HPE directly, or from an authorised reseller. (i.e. not from eBay)

A Solution

Noting that the problems documented as fixed by the update didn’t include mine, I continued to search websites for the specific error I was getting which was only shown by dmesg, not by tar, and found that when using tar with an LTO5 drive, the block size is essential.

The advise given here was you should use at least 256kb blocksize for an LTO5 drive.

So, almost like magic, adding the parameter “-b 512” (i.e. 512 x 512b = 256kb) to the tar command fixed the problem, and I’m now backing up to tape, but only after several hours of scouring the web and pulling my hair out.

Conclusion – the Moral of this Story

Tape backup is a whole order of magnitude more complicated and expensive than an external HDD or NAS drive. Don’t start down the road of tape unless you really need it, and can invest the time and energy in getting it to work properly.

Do your research thoroughly before buying anything, especially 2nd hand, and don’t assume just because you see something on the documentation that it will work without additional hardware and/or software.

Was it all worth it? Well, I hope I’ll never need to find out…