[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Escaping Data Rot

Michael J. Mahon wrote:
A bare LTO-2 drive should set you back about $100 from ePay, less if you frequent hamfests and computer swap meets. A lot of them are showing up on the retired equipment market and none that I've picked up are anywhere near their service limits in terms of POH or tape cycles (they all appear to have counters in non-volatile memory). 

All this reminds me of my use of DAT backup tapes in the early 1990s.
It was unusual (I was the only one I knew with a DAT drive), slow
(compared to hard disk rates), and inconvenient to use--particularly
for recovering, say, eight photos that I had accidentally overwritten.
Yes, the older rotary-head tape drives (DAT and 8mm) really gave tape backup a bad name. They were slow and unreliable. The LTO standard uses a fixed head with multiple tracks. The drives are capstan-less and rely on servo control to keep the linear tape velocity constant with a minimum of physical contact (man, do I wish that technology had been perfected back in the days when I used analog audio tape machines..)
An LTO-2 drive that's up to speed and streaming absorbs data at the full bandwidth of a U160 SCSI bus, and is not particularly slow with regard to transfer rate or random access (although obviously not in the same ballpark as a disk drive). I believe LTO-4 drives can absorb U320 bus speeds. 


Virtually all the volume of my data is already compressed: JPEGs and
MPEGs, so compression doesn't do me much good.  I have tens of thousands
of compressible files, but their combined volume is a small fraction of
the total.


So you'd be looking at the lower storage number, e.g. 200GB on LTO-2.


The problem, in most cases, is "stopping the world" or opening an
availability loss window for the shortest possible time.  Specialized
techniques are much better at this.
Yes, but we're digressing into areas that are not of concern to most of us on this list. Also, this is starting to drift off-topic, so I'll desist after this post. 


Sounds like a stiction problem, or possibly contamination.  Both are
extremely rare in modern drives, so that redundancy lowers the chance
of loss to a miniscule level.  Presumeably, RAID masked any loss of data
as a result of hardware failure.

In my experience (and there's been plenty of that ;-), most catastrophic
failures have nothing to do with disk hardware.  It is almost always an
errant program or operator that crashes the file system or database.
(And twice it was the hardware connection from the system to the drive.)

Modern disk drives provide abundant sensing of impending permanent
errors long before they actually occur, and keeping multiple copies
reduces risk of data loss below the level of "meteor collision" loss.
All I can say is that you must lead a very charmed existence :-). I have always used very high-end drives and have had plenty of them drop dead without any SMART warnings. Or, more commonly, simply refuse to spin up after a power down. Nowadays, that's more likely to be servo electronics than stiction, but it leaves you on the figurative side of the road just as surely! 

Anyway, I suggest everyone use what they're comfortable with.

Steve