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Over a period of three weeks, I experienced six complete failures of LTO-1 and LTO-2 tape drives at client sites. Some had failed mechanisms. Others lost the ability to write reliably. These were HP Ultrium 232, 448 and 460 drives. Most of these units were deployed between 2006 and 2008, so the timing of the failures is right. The capacities (400GB) are correct for the applications. I replaced a couple of drives with equivalent devices, just for consistency. One server also had a SCSI HBA failure, further delaying recovery. At that point, the customer asked if there were any hard disk solutions available that would be better (or less-finicky) than tape.

As I began to look for replacements, I discovered that the RDX removable disk storage technology has been adopted by the major server manufacturers (HP, Dell, IBM). From my perspective, it looks like docked 2.5" SATA disks connected either internally or externally via USB2 in capacities up-to 1TB. Since these are actual disks, it seems like recovery and seek time would be reasonable. But I have a few questions about the technology in practice.

  • Does anyone here use these drives with success? Is there anything to watch out for?
  • What differentiates RDX from straight external USB disks?
  • One of the advantages to tape in my application is that the drives have hardware compression. This helps immensely for the highly-compressive datasets I have to backup on Linux systems. Am I correct in assuming RDX relies on software compression?
  • Since these are physical disks, are there any mountpoint issues in Linux or Windows? One of the nice things about tape is that its not a mounted filesystem and typically isn't affected by viruses, rootkits, system crashes, etc.
  • In addition, I watched a primer on using RDX with Cactus Lone-Tar, and cringed when I saw them using a mkfs command to create a filesystem on the RDX drive at /dev/sda. Is there any chance of device renaming/reordering (from adding a SCSI controller, inserting a USB key, etc.), or will the docking unit persist at a particular device name as you swap drives?
  • Are the backup speeds of 30 megabytes/second accurate?

I'm curious, as this could be an interesting alternative. The series of tape drive failures came at a time where it makes sense to reevaluate other options before moving forward.

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I think that before looking at replacing one technology with another you should be looking at what caused the failures. Modern tape drives seldom fail that soon, so there may be other factors (dust, power spikes, etc.) that are the real issue and which may well give problems with the replacements as well. –  John Gardeniers Sep 24 '11 at 23:40
    
It's the age of the drives, tapes and the need for a SCSI or SAS HBA in these systems. I have about 120 installations out there, and the Ultrium/LTO drives tend to die at 3-5 years. Tapes begin to get stuck, the loading mechanism dies, I begin to get write errors, etc. This wasn't the result of an environmental issue. –  ewwhite Sep 25 '11 at 0:02
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I can confirm that "small" tape drives tend to fail miserably over time. I have seen a lot of DAT drives die after less than one year (yes, I know, DAT is mechanically challenging) and I yet have to see an LTO or DLT drive working flawlessly for more than 4 years when regularly in use. This may be different with drives in robotic autoloaders, I have no experience with that kind of gear. –  the-wabbit Sep 26 '11 at 22:35
    
BTW: with 120 sites it's probably a good idea to have the backups go to disk-based solutions and simply copy the backups off to a remote site instead of running around with tape cartridges around the building every day and hoping that they are restorable. Considering the fact that you are likely to have just one LTO drive per site there would be no way to test if the backup could be restored with different hardware in case of a full hardware failure. And even if you had different hardware to test with, a test restore would take too much time to do on a frequent, regular basis. –  the-wabbit Sep 26 '11 at 22:42
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@syneticon-dj, comparing DAT and LTO is like comparing a 50 year old Volkswagon to a late model BMW. DAT (Digital Audio Tape) technology wasn't even designed to be used for data backup. –  John Gardeniers Sep 28 '11 at 21:34
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2 Answers

up vote 7 down vote accepted

I looked long and hard at RDX drives and specified the embedded RDX units in a couple of Fujitsu servers I bought. Here's what I found:

  1. Microsoft native backup does not play nicely with RDX, because of the status of removable drives in MS disk management. As a result if you run Windows native backup (e.g. 2008 r2) you cannot send incremental backups to an RDX, only one-off full backups. If you want any nuanced handling of the backup you will need to write scripts.
  2. Ditto Microsoft Data Protection Manager does not recognise RDX, which is a shame because DPM is great even for small MS shops who might benefit from RDXs.
  3. Some people suggest a product called Firestreamer which lets you use RDX with DPM, but it's expensive and I found it to be a real pain to use and configure.
  4. I wanted a portable solution for both offsite recovery and archiving. RDX is okay for offsite recovery but for archiving the cost doesn't work. By archiving I mean taking point in time snapshots of the state of data (say every week or month) so that if I corruption is found then you can go back to the previous state.
  5. I bought about 4 300GB RDX drives at list price, but then around 12 120 GB drives on Ebay. This gave me enough drives to rotate media offsite, play with full system restore etc. for a small installation
  6. I have to say, that I never enjoyed restoring from RDX - times are about 20-30 MBps for the USB 2 version. You can get a SATA version which will make a slight improvement, or now a USB 3 version which do a lot better. If you are restoring images, the USB 2 version takes a long time. What I did like though was the fact that you could store a backup VHD on the RDX and boot that from the OS. I did this to restore a Hyper V virtual file server when its host disk became corrupted.
  7. I was waiting for Tandberg to release the RDX Quickstation autoloader, which there were rumours of at the beginning of 2010. Eventually I got fed up with waiting and bought Fujitsu LTO3 tape autoloader. This gives me loads of capacity, fast restore, no messing about with software issues, and cheap media. Also, backup software understands tape media rotation in a way that I never experienced using RDX.
  8. Tandberg have now released the RDX Quickstation and it looks pretty good - I like the fact that it uses the iSCSI protocol with an LTO3 tape emulator, because this means that it will work with virtualised backup software (which generally needs an iSCSI target to backup to tape, because most virtual systems do not give the virtual machine access to a host SCSI port or whatever you need to connect to a tape drive.) Although I like the look of it, and RDX drives are pretty good to handle, and it has speeds of around 70 MBPS, I'm still stuck on the fact that RDX drives are expensive. If you are just rotating 8 RDX drives then you're probably cool, but if you want to archive then you're not.
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This is excellent feedback. With the different interfaces, USB3 and eSATA, is the performance much better? It seems like the drive is the bottleneck at that point. –  ewwhite Sep 28 '11 at 4:31
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Thanks for the compliment. I checked and it's normal SATA not eSATA - so have updated my post accordingly. and according to the RDX storage alliance whitepaper, it only makes a slight (around 10 Mbps) improvmement over USB2. I've not seen benchmarks for the USB3 RDX, but I imagine and hope that it's substantially better. –  Mark Lawrence Sep 29 '11 at 13:01
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I found these two articles from itpro.co.uk and tom's hardware it seems they are better than tape.

The difference with USB is the mechanical way of working. RDX is probably faster and greater capacity. It also has an option to switch it to read only incase of accidents.

According to a few tests I saw the 30 MB/s is quite accurate, depending how many files you write and their size, they reached 28 MB/s .

The average lifetime is about 30 years in which 99% reliability according to Percept Labs.

And like you say IBM, HP and Dell use them do, if it is good enough for them, why not for you ? :)

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30MB/sec faster than tape? LTO4 can write at 120MB/sec if you can provide it data fast enough. –  SpacemanSpiff Sep 26 '11 at 3:25
    
I never said it was faster than tape, I said it has 30 MB/s according to the test, I never made a comparison to tape, I just answered his question : Are the backup speeds of 30 megabytes/second accurate? Learn to read :) –  Lucas Kauffman Sep 26 '11 at 8:21
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Was referring to your comment "it seems they are faster than tape", but later reference on writing at 30MB/sec. –  SpacemanSpiff Sep 26 '11 at 14:11
    
updated to better –  Lucas Kauffman Sep 26 '11 at 17:46
    
I can't tell what you're trying to say in this sentence: "The difference with USB is that is ofcourse the mechanical way of working, probably faster and greater capacity." –  sciurus Sep 26 '11 at 18:30
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