16 Aug
2008
16 Aug
'08
1:31 p.m.
On Fri, Aug 15, 2008 at 12:13 PM, Patrick Finnegan
<pat at computer-refuge.org> wrote:
On Friday 15 August 2008, Eric J Korpela wrote:
We got most of our tapes and drives donated from Fujifilm, and at
times Quantum and Compaq.
The vast majority of the tapes were Fujifilm. But even then, we had
brand new Fujifilm tapes occasionally kill a drive and few percent of
our tapes were "write only". Average lifetime of a drive was about a
year (of nearly continuous operation.)
On Thu, Aug 14, 2008 at 12:12 PM, Jules
Richardson
If you think that DLT was unreliable, you must have had bad (Imation)
tapes, tried to use DLT8000 or cheap-o DLT-1 drives. We had very few
problems with Fujifilm tapes, and DLT7000 drives... Yep - there was an awful lot of proprietary stuff
out there.
Personally I'm a DLT fan - like you say, it's expensive, but it's
worth it for the reliability.
I'm totally off tape. Our experience with DLT is that the drives
don't last, transfer rates are too slow, and the media are too
unreliable and too expensive. Haven't tried LTO Ultrium, but for
$1700 for a drive and $40 for a 400GB (uncompressed) tape it's too
expensive when you can get 750GB SATA drives for $150. (The
crossover point is 17TB). Our compression rate is at least 1.5:1 on average,
we've found too.
Unsurprisingly, the compression you'll get will be almost exactly the
same that gzip will give you if you're streaming to disk. Compression
is a software function.
I also think that comparing the cheapest possible SATA
drives to
high-end LTO tapes is a bit like apples to oranges; you might as well
compare LTO drives to $1/GB FC/SAS disks, which have a similar market,
reliability, and speed.
You're buying into somebody's marketing. In actual use FC, SCSI and
SAS disks have failure rates that are nearly identical to SATA and ATA
drives for 7500 RPM drives. In our experience failure rates go up
with the drive rotation rate, although I have not seen a study of
that. The only reason you would choose to pay extra for SCSI/FC/SAS
is to get the faster rotation rate. The reason that manufacturers
don't offer 10K and 15K RPM drives in SATA and ATA is that people
probably won't pay as high a premium as they will with SCSI and FC.
In terms of failures of communication between the controllers and the
drives, FC over fiber is the wost ever. We multipath all fiberchannel
devices because controllers have a tendency to freeze on any error.
SCSI is getting worse as time goes on because the connectors keep
getting smaller and weaker. We also multipath anything with VHDCI
connectors.
Also, if you want to complain about speed, it's
hard to find a single
disk that can keep up with the streaming speed of a new LTO-4 tape
drive..
If you buy one of those who can afford a disk? Anyway if you're
backing to 800GB tapes it's pretty unlikely it's coming off a single
disk.
Eric