Why online disk storage is not the same as using tapes

A couple of years ago I posted about an unlucky encounter with my Thecus N5200 Pro. On the 1st January at 06:15 I had a New Year’s present. A disk died on me. The Thecus duly notified me by starting to beep.

I still have my RAID-6 setup so there was no real problem. I have 2 redundant disks. So I went and bought a replacement and fitted it and the Thecus duly started rebuilding the RAID array with an estimated time to finish of about 1 day (5x1TB disks, so ~3TB array).

Disk prices have increased significantly since I originally bought my array but buying a single disk was not a problem.  During the time that the array was rebuilding or shortly afterwards however a second disk failed just as it had 2 years ago when I ended up losing my array as the RAID-5 setup did not have any further disks. This time however there was no problem. RAID-6 saved me and the photos and backup information I had on my Thecus so I was happy and I ended up running out and buying another disk. This one triggered the array rebuild and completed successfully.

That lead me to think. A lot of people push the move to external disks as a backup alternative. Certainly this gives you online information and generally works well. I am using this device at home to keep my photos and other files and also to do a backup of my main machine to a separate location.  However, what strikes me as being clear: replacing disks is expensive. Had I been using tapes for backups throwing away the 2 tapes and buying new ones would have been much cheaper than buying 2 new hard disks for my array.  Of course a disk array does not provide you a site backup and also does not provide you a convenient way to store multiple backups over time. For that it is not yet cost effective.

So after this experience I am tempted to look and see if there are any small tape devices which I could attach to my PC and use that to give me these extra facilities. The hardware no doubt exists but from previous searches it is expensive and out of the price range of the average home user. That is a shame.  With a lot of people now dismissing tape devices as old fashioned failure of drives in a small array like my 5-disk array may turn out to be pretty expensive (in money) or pretty costly (lost data).  RAID-1 or RAID-5 sound great but can you afford for a second disk to fail while the array is rebuilding after the first disk has failed? If you can not then arrays of this type may not be for you and may lead you to a false sense of security.

The title of my original post was Unlucky Encounter… So have I just been unlucky (again) or is this sort of problem something which has happened to more people?

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Simon J Mudd

Born in England, I now live in Spain, but spent a few years living in the Netherlands. I previously worked in banking (financial markets) both in IT and as a broker, but IT has always had a stronger influence. Now working at booking.com as a Senior Database Administrator. Other interests include photography, and travel. Simon is married, with two children and lives in Madrid.

2 thoughts on “Why online disk storage is not the same as using tapes”

  1. Given that 1-2TB drives are relatively inexpensive these days, it may just be cheaper to go grab a few external USB drives and store your data on them, connecting them only when you need to do a backup or restore. Another option is to look into file systems that handle redundancy and can version for you maybe like HDFS. No guarantees that either will meet your specific needs, however.

  2. Your story is such a common one. RAIDs are excellent for resisting some degree of hardware failure but in my opinion the fist thing that should always be done before a failed drive in the array is replaced is to download the most critical data (even if it is just to a memory stick). Too often a second (or in the case of RAID6 a third) drive will fail during the re-build. This is not too surprising, typically all of the drives in the array will have been made in the same factory on the same day and have all spent their lives in an identical operating enviroment, whatever caused one drive to fail will very likely bring down more of them shortly afterwards.

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