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Re: Implementing virtual memory on cassette tape

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Alex McDonald <blog@rivadpm.com> writes:
>On Aug 8, 1:24=A0pm, an...@mips.complang.tuwien.ac.at (Anton Ertl)
>wrote:
>> Alex McDonald <b...@rivadpm.com> writes:
[...]
>Then the best of luck getting DHL to deliver your 4TB drive in one
>piece.

The drives are delivered to us in one piece, why wouldn't they
delivered elsewhere in one piece.

>> >In general,
>> >drives don't like being spun up; they fail much more quickly than
>> >disks that are spun throughout their entire lives.
>>
>> Not in my experience. =A0We have a backup server that spins down idle
>> disks, and have not noticed any reliability problems. =A0And we have not
>> noticed reliability problems with our off-line storage disks, either.
>> So disk spin-down is practical, and, in our experience, reliable.
>
>Yes, you're one of the lucky devils that I meet; but much less
>frequently than I used to, since the advent of super large SATA
>drives. The stats speak for themselves; failure rates of SATA drives
>are in the ones and twos of % per annum, and if you have an array with
>a couple of hundred plus, failure is to be expected and needs to be
>managed.

Sure, hard disks fail now and then.  And we certainly have organized
our backups such that the failure of one or two drives does not lead
to catastrophic loss.

>It's not just that the drive fails to spin up, or dies with a
>catastrophic failure in operation either. Bit error rates per byte
>haven't changed in 10 years, but the size of drives has grown
>exponentially. Every 4TB drives will have, on average, several
>correctly sent but badly written blocks, and a number of blocks where
>the drive declared that it had -- honest! -- written your data but
>hadn't. You just haven't found those corrupt or silent blocks yet.
>Spin down & up exacerbates these problems.

Sounds like you swallowed some horror stories some people like to
spin.  Why should spin down exacerbate these problems?

BTW, in my experience (based on several occasions) the most frequent
cause of corrupted disk blocks is due to misdesigned drives that do not
react correctly to power fluctuations.

>> I never heard about MAID and COPAN before, but it seems that this was
>> not sold as a backup solution, but as main storage. =A0There, I agree,
>> it is not very practical for most uses, and spin-slow is better.
>
>It was sold as backup; the systems couldn't support all the disks
>spinning at the same time.

The latter is true.  But according to
<http://wikibon.org/blog/copan-may-be-dead-but-maid-isnt/>, this was
sold as main storage.

>To get adequate bandwidth, data needs to be striped across several 10s
>of disks, and everyone wants to do their backups at the same time. But
>the COPAN power supplies were inadequate to support all the disks.
>It's the economics of competing with tape; big power supplies to
>support 480 disks packed in a single rack cost lots of money.

If you need that much bandwidth from your backup system, the tape
solution needs a similar number of tape drives (because tape drives
have a similar bandwidth), and the cost of that would dwarf the costs
of everything in the disk system, including a power supply for
spinning all the disks.  And these tape drives would need an even more
powerful power supply: Looking at
<https://iq.quantum.com/exLink.asp?8078910OS53M15I46299120>, idle
power consumption is 6.5W, typical 21.4W, peak 30.2W, i.e., about 2-3
times of a hard disk drive.

And how are you getting all this bandwidth to and from the backup
system?  480 disks with, say, 150MB/s each means 72000MB/s.

> Then,
>when data is required for restore, lots of disks have to be spun down,
>and others spun up, an activity that draws a lot of juice; it takes as
>much power to spin up a disk as running it for several minutes.

<http://www.seagate.com/files/staticfiles/docs/pdf/de-DE/datasheet/disc/barracuda-ds1737-1-1111de.pdf>
lists a power-up power consumption of at most 2A @12V, i.e., 24W (my
own measurements are in the same ballpark), and an average power
consumption of 8W for the 3TB model.  It takes about 10s to spin up a
drive, so spinning up takes as much as running a disk for half a
minute.

> And it
>takes 10s of minutes to do so as they can't all be powered up at
>once.

With the power supply you would need for the 480 tape
drives, yes, you could spin them all up at the same time.  But this is
typically not needed, certainly not for a saner backup management (but
neither are the 480 tape drives).

>For users that want to do restores quickly, it's useless. The power
>economics vs the high latency, low bandwidth & inconvenience just
>don't stack up.

Tape loses in power, latency, bandwidth, and convenience.  The only
thing where it wins is cost for low-bandwidth high-capacity storage.
Taking the numbers from my price watch site, I get:

EUR 46/TB for external 3TB disks (similar price for internal disks)
EUR 1311 for an internal LTO-5 tape drive (>1700 for external)
EUR 41 for a 1.5TB LTO-5 tape (EUR27/TB)

the crossover is at about 69 TB per tape drive (higher if you use
external tape drives).  If you want reliable and timely access to your
tapes, you need at least two tape drives, so tape is only cheaper if
you want to store more than 138TB on it (and even then it still has
all the other disadvantages).

>For the occasional server with a handful of disk
>drives, it's not so much of a problem, but at scale, even a moderate
>scale in the 10s of TB range, it's unworkable.

That's nonsense.

>Again, the power economics
>don't make sense for main storage where a complete stripe of 10s or
>more of them need spun up to get at a single 4K file.

Yes, striping (RAID-0) a 4KB file across tens of disks does not make
sense.

>Believe me, you're gambling with your
>current backup strategy...)

The only thing you know about our current backup strategy is that we
use disks and spin-down.  If by "gambling" you mean that we are
relying on luck, no, not much.  Of course there is the possibility
that everything fails at the same time, but that possibility is not
exclusive to disk drives.  Actually the probability that two tape
drives fail before we get a replacement is much higher than the
probability that all the disks on which we have our backups fail
between two backups.

- anton
-- 
M. Anton Ertl  http://www.complang.tuwien.ac.at/anton/home.html
comp.lang.forth FAQs: http://www.complang.tuwien.ac.at/forth/faq/toc.html
     New standard: http://www.forth200x.org/forth200x.html
   EuroForth 2012: http://www.euroforth.org/ef12/

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Implementing virtual memory on cassette tape chitselb <chitselb@gmail.com> - 2012-08-07 06:21 -0700
  Re: Implementing virtual memory on cassette tape Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-08-07 08:44 -0500
  Re: Implementing virtual memory on cassette tape anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-08-07 14:01 +0000
  Re: Implementing virtual memory on cassette tape Mark Wills <markrobertwills@yahoo.co.uk> - 2012-08-07 07:24 -0700
  Re: Implementing virtual memory on cassette tape Stan Barr <plan.b@dsl.pipex.com> - 2012-08-07 15:30 +0000
    Re: Implementing virtual memory on cassette tape Stan Barr <plan.b@dsl.pipex.com> - 2012-08-07 17:36 +0000
  Re: Implementing virtual memory on cassette tape Jason Damisch <jasondamisch@yahoo.com> - 2012-08-07 11:52 -0700
    Re: Implementing virtual memory on cassette tape Paul Rubin <no.email@nospam.invalid> - 2012-08-07 12:39 -0700
      Re: Implementing virtual memory on cassette tape Paul Rubin <no.email@nospam.invalid> - 2012-08-07 12:55 -0700
        Re: Implementing virtual memory on cassette tape Bernd Paysan <bernd.paysan@gmx.de> - 2012-08-07 22:00 +0200
          Re: Implementing virtual memory on cassette tape Paul Rubin <no.email@nospam.invalid> - 2012-08-08 00:27 -0700
            Re: Implementing virtual memory on cassette tape Mark Wills <markrobertwills@yahoo.co.uk> - 2012-08-08 01:26 -0700
              Re: Implementing virtual memory on cassette tape Alex McDonald <blog@rivadpm.com> - 2012-08-08 02:31 -0700
              Re: Implementing virtual memory on cassette tape Paul Rubin <no.email@nospam.invalid> - 2012-08-08 02:46 -0700
            Re: Implementing virtual memory on cassette tape Alex McDonald <blog@rivadpm.com> - 2012-08-08 02:23 -0700
              Re: Implementing virtual memory on cassette tape anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-08-08 10:57 +0000
                Re: Implementing virtual memory on cassette tape Alex McDonald <blog@rivadpm.com> - 2012-08-08 04:59 -0700
                Re: Implementing virtual memory on cassette tape anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-08-08 12:24 +0000
                Re: Implementing virtual memory on cassette tape Alex McDonald <blog@rivadpm.com> - 2012-08-08 11:10 -0700
                Re: Implementing virtual memory on cassette tape Bernd Paysan <bernd.paysan@gmx.de> - 2012-08-09 00:13 +0200
                Re: Implementing virtual memory on cassette tape Alex McDonald <blog@rivadpm.com> - 2012-08-08 16:05 -0700
                Re: Implementing virtual memory on cassette tape Paul Rubin <no.email@nospam.invalid> - 2012-08-08 17:30 -0700
                Re: Implementing virtual memory on cassette tape Bernd Paysan <bernd.paysan@gmx.de> - 2012-08-09 03:26 +0200
                Re: Implementing virtual memory on cassette tape Alex McDonald <blog@rivadpm.com> - 2012-08-09 05:30 -0700
                Re: Implementing virtual memory on cassette tape Bernd Paysan <bernd.paysan@gmx.de> - 2012-08-09 19:21 +0200
                Re: Implementing virtual memory on cassette tape Alex McDonald <blog@rivadpm.com> - 2012-08-09 13:30 -0700
                Re: Implementing virtual memory on cassette tape Bernd Paysan <bernd.paysan@gmx.de> - 2012-08-10 01:27 +0200
                Re: Implementing virtual memory on cassette tape vandys@vsta.org - 2012-08-09 00:32 +0000
                Re: Implementing virtual memory on cassette tape Bernd Paysan <bernd.paysan@gmx.de> - 2012-08-09 03:33 +0200
                Re: Implementing virtual memory on cassette tape anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-08-09 06:00 +0000
                Re: Implementing virtual memory on cassette tape Alex McDonald <blog@rivadpm.com> - 2012-08-09 05:26 -0700
                Re: Implementing virtual memory on cassette tape anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-08-09 13:44 +0000
                Re: Implementing virtual memory on cassette tape Alex McDonald <blog@rivadpm.com> - 2012-08-09 10:21 -0700
                Re: Implementing virtual memory on cassette tape Bernd Paysan <bernd.paysan@gmx.de> - 2012-08-09 19:50 +0200
                Re: Implementing virtual memory on cassette tape Alex McDonald <blog@rivadpm.com> - 2012-08-09 12:32 -0700
                Re: Implementing virtual memory on cassette tape Bernd Paysan <bernd.paysan@gmx.de> - 2012-08-09 22:07 +0200
                Re: Implementing virtual memory on cassette tape Alex McDonald <blog@rivadpm.com> - 2012-08-09 13:58 -0700
                Re: Implementing virtual memory on cassette tape Paul Rubin <no.email@nospam.invalid> - 2012-08-09 17:36 -0700
                Re: Implementing virtual memory on cassette tape Alex McDonald <blog@rivadpm.com> - 2012-08-10 04:13 -0700
                Re: Implementing virtual memory on cassette tape Paul Rubin <no.email@nospam.invalid> - 2012-08-11 20:27 -0700
                Re: Implementing virtual memory on cassette tape anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-08-10 15:57 +0000
                Re: Implementing virtual memory on cassette tape Alex McDonald <blog@rivadpm.com> - 2012-08-13 05:23 -0700
                Re: Implementing virtual memory on cassette tape anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-08-15 15:13 +0000
                Re: Implementing virtual memory on cassette tape Alex McDonald <blog@rivadpm.com> - 2012-08-15 11:57 -0700
      Re: Implementing virtual memory on cassette tape anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-08-08 07:08 +0000
        Re: Implementing virtual memory on cassette tape chitselb <chitselb@gmail.com> - 2012-08-08 06:25 -0700
      Re: Implementing virtual memory on cassette tape Mark Wills <markrobertwills@yahoo.co.uk> - 2012-08-08 01:23 -0700
      Re: Implementing virtual memory on cassette tape kenney@cix.compulink.co.uk - 2012-08-08 05:06 -0500
  Re: Implementing virtual memory on cassette tape Percy <percival.andrews@gmail.com> - 2012-08-08 21:11 -0700
    Re: Implementing virtual memory on cassette tape chitselb <chitselb@gmail.com> - 2012-08-08 21:30 -0700
      Re: Implementing virtual memory on cassette tape percival.andrews@gmail.com - 2012-08-08 23:50 -0700
        Re: Implementing virtual memory on cassette tape chitselb <chitselb@gmail.com> - 2012-08-09 03:54 -0700
          Re: Implementing virtual memory on cassette tape Paul Rubin <no.email@nospam.invalid> - 2012-08-09 09:07 -0700
            Re: Implementing virtual memory on cassette tape chitselb <chitselb@gmail.com> - 2012-08-09 12:20 -0700
  Re: Implementing virtual memory on cassette tape Mat <dambere@web.de> - 2012-08-10 13:41 -0700
    Re: Implementing virtual memory on cassette tape Coos Haak <chforth@hccnet.nl> - 2012-08-10 23:54 +0200
      Re: Implementing virtual memory on cassette tape dambere@web.de - 2012-08-10 15:41 -0700
        Re: Implementing virtual memory on cassette tape Coos Haak <chforth@hccnet.nl> - 2012-08-11 01:47 +0200
    Re: Implementing virtual memory on cassette tape Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-08-11 03:50 -0500
      Re: Implementing virtual memory on cassette tape anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-08-11 09:03 +0000
        Re: Implementing virtual memory on cassette tape Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-08-11 16:08 -0500
    Re: Implementing virtual memory on cassette tape "Elizabeth D. Rather" <erather@forth.com> - 2012-08-11 21:51 -1000

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