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Re: Implementing virtual memory on cassette tape

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Alex McDonald <blog@rivadpm.com> writes:
>On Aug 9, 7:00=A0am, an...@mips.complang.tuwien.ac.at (Anton Ertl)
>wrote:
>> Alex McDonald <b...@rivadpm.com> writes:
>> >On Aug 8, 1:24=3DA0pm, 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.
>
>They don't contain your data.

So what?  If it's broken, I send another one; it's a backup.  It's
redundant, and it's definitely not the only backup.

>> Sounds like you swallowed some horror stories some people like to
>> spin. =A0Why should spin down exacerbate these problems?
>
>Several reasons.
>
>Rated start/stop cycles; 250 average on/off cycles per year at the
>expected population AFR of 0.55% (Seagate Cheetah 15.7, enterprise
>class drive).

What does AFR have to do with the horror stories about corrupted data?
And anyone who uses "enterprise class" drives for backup has too much
money.

>Low temperature operation; the AFR increases significantly (5 times
>the AFR at <20C to those running >40C, Google study on 100000 desktop
>class drives), and spun down drives will be cooler during early hours
>of operation.

Fortunately even our spun-down drives have a higher temperature.  And
again, what does AFR have to do with your horror stories about
corrupted data?

>Slow spin; heads are designed for flight at a given RPM. Slow spin
>reduces the air cushion/head height and makes the drives more
>susceptible to shock. Even at full speed they can be shouted into
>submission; http://www.youtube.com/watch?v=3DtDacjrSCeq4&feature=3Dplayer_e=
>mbedded

What do head crashes resulting from shock have to do with the horror
stories about corrupted data?

>Due to commercial NDAs and other reasons, I can't do any better than
>point you at what is publicly available. Our AFRs are much lower for a
>variety of reasons; dual parity RAID

How does RAID make individual drives more reliable?

>> 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.
>
>That is rarely a problem on a well designed storage array, where the
>power management is more sophisticated than that of a server. Pulling
>the plug on such a system should have no deleterious effects.

It's also not a problem for well-designed disk drives, but yes, to
some extent the power supply can alleviate the problems coming from
misdesigned drives; but if the problem is between the power supply and
the drive (i.e., a suboptimal power connection), the misdesigned drive
will still produce corrupt blocks.

>> > 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/dis...=
>>
>> 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. =A0It takes about 10s to spin up a
>> drive, so spinning up takes as much as running a disk for half a
>> minute.
>
>Drives vary; SATA drives at 5k RPM spin up faster than high RPM SAS
>drives at 15K, which may take minutes to stabilize at operating speed.
>During that time, the disk isn't usable, and I stand by my assertion
>that spin up wastes as much power as several minutes of full
>operation.

Sure, if a drive takes several minutes to spin up, it will consume as
much power as several minutes of full operation.

But who in his right mind uses an expensive and power-hungry high-RPM
drive that takes forever to spin up for a storage solution that
requires low power and fast spin-up?  Ok, a sales guy selling to a
clueless and rich customer will do it, but not because of technical
merit.

>> With the power supply you would need for the 480 tape
>> drives, yes, you could spin them all up at the same time. =A0But this is
>> typically not needed, certainly not for a saner backup management (but
>> neither are the 480 tape drives).
>
>I don't know where you got the idea that 480 tape drives was the
>equivalent to 480 disk drives, but it's not an assertion I made and
>certainly qualifies as insane.

You claimed that lots of disks had to be spun up for bandwidth
reasons, and you wrote:

|It's the economics of competing with tape; big power supplies to
|support 480 disks packed in a single rack cost lots of money.

which suggest that you think that a backup solution needs 480 disks
spun up for bandwidth reasons.

>> >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.
>
>Why? The limiting factor isn't the disk or tape that you're backing up
>to, but how fast you can shovel it off the server.

It's nonsense, because we are backing up to disks with a total of 10s
of TB, and it's workable, and if we wanted to back up to more disks,
we would just use more disks.  And the main bandwidth limit is, as you
write, getting the data off the main storage.

>> >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.
>
>Ignoring RAID-0, since RAID-any systems also stripe,

RAID-1 doesn't.

>the problem is
>that such files do get spread across an unknown number of disks.

With typical block sizes, a 4KB block is not distributed across
multiple disks, even with RAID-0.

>They
>all need fired up to find even the smallest file, since it's not just
>the file, but the meta data that needs accessed too.

Meta data is often in OS caches, at least on decent OSs.

But yes, I agree that spin-down is not practical for main storage; but
from what I read, the idea of COPAN was to make it practical by
rearranging data such that frequently-accessed data resides on a few
drives.  Anyway, for backups spin-down is totally practical, certainly
the way we do our backups.  When the backup is written (or read), the
disk spins up, and some time after the access, it spins down.

- 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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