Data Storage - Need help on Tape,Optical disk...

Author

Need help on Tape,Optical disk...

babi

2006-05-15, 7:12 am

Hi,
Right now we are looking for the relaibility study of the disk, tape,
magneto-optic disk etc. which are primarily involve in the mass
storage.
Our requirement is any of the tape or above device data to predict the
relaibility.
I'll deeply appriciate if anyone can help me out to get the data or
pointer.

Thanks & Regds,
Babi

Faeandar

2006-05-19, 1:14 am

On 14 May 2006 23:45:15 -0700, "babi" <tmohanta@gmail.com> wrote:

>Hi,
> Right now we are looking for the relaibility study of the disk, tape,
>magneto-optic disk etc. which are primarily involve in the mass
>storage.
>Our requirement is any of the tape or above device data to predict the
>relaibility.
>I'll deeply appriciate if anyone can help me out to get the data or
>pointer.
>
>Thanks & Regds,
>Babi

Well, I believe plenty of studies have been done that show tape and
optical are more reliable than disk. However, it's alot simpler to
put disk in a raid and make the overall architecure much more
reliable.

But from a pure media viewpoint disk is the least reliable of the 3.

~F

backupmeister@gmail.com

2006-05-23, 1:13 am

Not sure if I agree with everything Faeandar said, but I do agree in
part. The big advantage that disks have over tape or optical is that
you can put them in a RAID array to essentially remove any concerns
about reliability. No longer will the loss of a single piece of media
cause your storage process to fail.

I don't share Faeandar's opinion that tapes and optical are far more
reliable than disks. While I don't have a lot of experience with
optical, I do have extensive experience with both disk and tape in many
people's environments. If disks failed anywhere as often as tapes do,
most people I know would throw them out.

My personal opinion is that this unreliability comes from two things.
The first is the fact that tape (and optical) systems are open systems,
where the media must be injected and ejected from the drive,
introducing contaminants each time. Disk drives, on the other hand,
are closed systems -- no contaminants ever. In addition, the physical
media of tape (and some optical) is inherently more "wimpy" than the
media used in a disk drive. Disks can also handle more g-forces than
most tape cartridges I use on a regular basis. Drop a DLT or LTO
cartridge from shoulder-height, and you can expect some parts to come
flying off inside. In comparison, a powered-off disk drive could
handle a similar fall much easier.

Now... Power off a disk drive and set it on a shelf next to an ejected
tape drive and leave it there for five years. I'll trust the tape
every time in that scenario, as disks were not intended to be left
powered off that long with data.

The second reason that tape is less reliable is that people don't
stream their tape drives. They're sending 5 MB/s to a 60 MB/s drive,
or 10 MB/s to a 150 MB/s tape drive. The thing's constantly stopping
and starting, going into drive, then reverse, then drive, then reverse.
You do this enough, and you'll fail too. In contrast, disk drives can
go any speed you want them to. You want 150 MB/s? Fine. You want 1
KB/s? That's fine, too. Tape drives can't say that. The result is
really unreliable tape drives.

The proof's in the pudding. I've watched company after company convert
from tape to disk for backups, and they've watched their success rates
skyrocket. Is that because tapes were less reliable, or just because
disk is a better match for how backups behave? Either way, in a
real-world scenario, disks trump -- and disks in a RAID array trump
even further.

Now, as to optical, I don't have any data. I'm all about backups, and
people just don't use optical for backups -- the transfer rates simply
aren't high enough. I think we've finally reached double digits with
some of the formats, but the numbers are still way behind those of tape
or disk. However, if I had to store something on a media that I was
going to store for 7+ years, I'd use optical in a heartbeat.

Jeff Jonas

2006-06-06, 1:16 am

>Now... Power off a disk drive and set it on a shelf next to an ejected
>tape drive and leave it there for five years. I'll trust the tape
>every time in that scenario, as disks were not intended to be left
>powered off that long with data.

I look around my collection-o-stuff and my crystal ball is definitely faulty.

The density of DVDs is alluring but a Library of Congress report
concerning data longevity didn't suggest any recordable DVDs
until the mfgrs give sufficient information about the formulation.
Only certain recordable CD formulations were recommended for archival use.
I record the md5sums of all files on CDs and DVDs I burn
so I can verify the medium.

Hard drives: yes, I have hard drives with data on them,
but plugging them in is hard when they're old interfaces:
High Voltage SCSI differential, ESDI, MFM/ST506, SMD.
The USB adapters only support ATAPI/IDE with DMA
(older drives don't work with them).
Most internal removeable trays (IDE or SCSI) are not hot-swap.

Tapes: I have no access to magtapes anymore.
Who could imagine that they'd all disappear
after being around for what: 50 years?
Data on videotapes: that format died fast.
The large QIC tapes surprised me:
most drives still read the old formats
and the drive interface evolved
from QIC-36 to QIC-02 to SCSI.
That's a lovely thing about tapes:
the drives evolve to new speeds and interfaces
but usually remain backward-compatible
if the tape physically fits the drive.

Floppy disks: need I say that's a dead format,
particularly any non-FAT file system such as
those used for proprietory word processing systems.

Punched cards, paper tape: I can't find readers ANYWHERE anymore.
But at least they're human readable and can be scanned.

Which means that good old fashined printouts are still a reasonable
format: they're human readable, can be scanned/OCR,
and acid free paper lasts for hundreds of years.

Gaaah! It's a lose/lose situation :-(
--

-- mejeep deMeep ferret!