On Saturday 06 March 2010, Jon LaBadie wrote:
>On Fri, Mar 05, 2010 at 07:44:32PM -0500, rory_f wrote:
>> Jon LaBadie wrote:
>> > On Fri, Mar 05, 2010 at 02:57:01PM -0500, rory_f wrote:
>> > > Hey guys. Thanks
>> > >
>> > > I checked my library GUI and for the tape run i was just talking
>> > > about, where it was stopping around 230gb, it seems compression WAS
>> > > on. I turned it off via mt and now the gui says "off" (after stopping
>> > > the run obviously)
>> > >
>> > > I was *sure* i turned it off with mt before. Im doing another
>> > > amtapetype now.
>> > >
>> > > And the comment regarding labeling: thanks. I'll most certainly
>> > > relabel all the tapes after this tapetype is done.
>> > >
>> > > Thanks again guys.
>> >
>> > Recalling your data in the original posting I think an amtapetype run
>> > was estimated to take about 8 hours. I think LTO drives are capable of
>> > writing a full tape in about 1.5 hrs, amtapetype should do two full
>> > writes, thus about 3+ hours total.
>> >
>> > As you system seems to be writing at less than 1/2 full speed, I wonder
>> > if it is failing to stream. If an LTO drive is not streaming, is its
>> > capacity affected by having large gaps caused by the start and stopping
>> > action?
>>
>> ok, so here is the latest one.
>>
>> [ama...@backup tor]$ amtapetype -o -f /dev/nst0 -e 400G
>> Writing 1024 Mbyte compresseable data: 32 sec
>> Writing 1024 Mbyte uncompresseable data: 32 sec
>> Estimated time to write 2 * 409600 Mbyte: 25600 sec = 7 h 6 min
>> wrote 6815744 32 Kb blocks in 52 files in 5733 seconds (No space left on
>> device) wrote 6815744 32 Kb blocks in 104 files in 5959 seconds (No space
>> left on device) define tapetype unknown-tapetype {
>> comment "just produced by tapetype prog (hardware compression off)"
>> length 212992 mbytes
>> filemark 0 kbytes
>> speed 37322 kps
>> }
>>
>> compression was set OFF in the gui for the library interfacing with the
>> drive.
>>
>> so, it seems, unless these tapes i have here are all pooched, the drive
>> is giving me problems. ugh.
>>
>> i'd try it on our other drive but ... that's out being replaced ;-).
>> maybe it's time to get this replaced too, while i still have the
>> maintenance contract.
>>
>> thanks for the help.. any further input on this is greatly appreciated!
>
>When the other drive was sent out for maintenance, perhaps the cableing was
>changed or disturbed.
>
>With SCSI it is always a good idea to check hardware, card, cables,
> terminators, etc. Try reseating, replacing, changing order, ...
>
>jl
>
Refresher course 101 on scsi here folks, bear with me.
Because the scsi buss is a transmission line, and demands a decent VSWR,
there are 2 things to remember when dealing with scsi.
1. A list of pre-requisites that must be met if it is to work:
1.a: termination power, it has to come from someplace, preferably the host
controller.
1.b: terminations can only be at the ends of the cable, one and exactly one
on each end. Leaving a 6" pigtail hanging out because you removed the drive
on the end of the cable, and which co-incidentally also was the terminating
device is a more common mistake than one would think.
1.c: when supplying scsi term power, there needs to be an isolation diode
between the supply and the term power line in the cable, pointed so that the
voltage can get to the cable ok, but cannot be fed back into an accessory
device after it has powered the terminators on that device.
1.d: Because this diode has a voltage drop, and the original idiots (yes,
that _is_ the right terminology) chose the resistor values based on std
values AND a 5 volt supply, so a common silicon diode virtually cannot be
used if the scsi bus is to be error free. The .65 to .7 volts of drop in an
Si diode reduces the logic one voltages noise margin by about 2/3rds. from
the target of 3.0 volts, but usually about 2.85 due to the resistors chosen,
throw in the .7 loss of the diode divided by the resistor ratio's (330 to
ground, 220 to the 5 volt line, and your logic 1 noise margin is whats left
after you subtract the 2.4 volts of a guaranteed logic 1. At 2.7 volts it
might work if the resistor tolerance are spot on. At 2.55 volts, you have
only a 150 millivolt noise margin and you may as well hold a seance, its
dead, Jim. Therefore this diode must be either a power germanium or a
schotkey rated for the current in order to get a decently low forward voltage
drop. Otherwise find a 6 volt supply for termination power. TBT, when the
psu voltage in the host machine is starting to sag in its old age, and is
already 200 millivolts low, I've been known to go get a 6 volt dc wall wart
from the shack and use that. It Just Works(TM). FWIW, I have yet to see a
Ge or Schotkey diode used on any of the major scsi vendors cards, so don't
assume that just because it says Adaptec on it, it can't be wrong. And it is
precisely those cards I've had to wall wart power several times.
If you've done all that & it still doesn't work, have a tech with a 100+ mhz
scope look at it to see why the signal echos (aka VSWR) are so bad. Maybe
you've got one bad resistor in the termination packs, so check all active
lines, 21 of them in a 50 wire scsi-II cable IIRC. Make sure he understands
exactly what the term 'VSWR' means, a great many don't, somehow thinking it
only applies to continuous wave radio/tv transmitters. VSWR is VSWR whether
its digital, or CW, its still VSWR.
2: Alternatively, you can advertise for a virgin to be sacrificed. It won't
help of course. And its a terrible waste considering how hard it is to find
one these days.
--
Cheers, Gene
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Reality is bad enough, why should I tell the truth?
-- Patrick Sky
