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Re: Question: SSD speed

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On 10/8/2020 5:13 PM, Stefan Monnier wrote:
>> 	a container nears being full.  If one has 1 MB of storage available
>> 	(allowing for file system overhead and block alignment), then 1 MB
>> 	of data will fit, but 1 MiB will not.
> 
> In which way is the KB-vs-KiB discrepancy different from the "file
> system overhead and block alignment"?

	File system overhead is not primarily an artifact of the size of the 
blocks.  Block alignment is related to the size of the blocks, but then 
I never said it was not.

> Maybe it's a higher percentage, but the end result is the same: if your
> FS says you have N bytes left, it does not guarantee you that an N byte
> file will fit,

	If it says you have 1.00 MB free, then it is guaranteed 1.00 MiB will 
not fit.  If it (accurately) says you have 1.00 MiB free, then 1.00 MB 
is indeed guaranteed to fit.

> so you need to include some slack.

	Not usually that much.  Again, it depends on the situation.

> And since very few
> people are able to quickly compute how many blocks are needed for
> a file of size N on the specific filesystem they use, you're better off
> using a "safe enough" estimate.  This notion of "safe" enough is one
> learned empirically over the years, so whether it's 2% or 10% doesn't
> really matter that much, as long as it's pretty much always the same.

	Well, the point is it isn't the same.  One PiB is 1,125,899,906,842,624 
bytes.  One PB is 1,000,000,000,000,000 bytes.  That is a difference of 
12.6%, vs. 2.4% difference between 1 KiB and 1 KB.


>> As an engineer, precision is absolutely of the essence.
> 
> When talking about the capacity of mass storage, you don't need
> precision, since it just has to be large enough, rather than having to
> have exactly the right size.

	Indubitably, but a 12.6% shortfall would be a problem.

> Engineers are very familiar with such imprecise constraint and with
> the use of safety margins to account for them.

	Of course I am.  There are plenty of cases where a safety margin is 
required.  There are plenty of other cases where a tiny differential can 
mean the difference between working well and a catastrophic failure. 
Direction also matters.  A cylinder that is just 0.001 mm oversize will 
not fit in a hole that is 0.001 mm undersize.

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Question: SSD speed Hans <hans.ullrich@loop.de> - 2020-10-07 10:50 +0200
  Re: Question: SSD speed Georgi Naplatanov <gosho@oles.biz> - 2020-10-07 11:40 +0200
  Re: Question: SSD speed Steve McIntyre <steve@einval.com> - 2020-10-07 12:00 +0200
  Re: Question: SSD speed "Jeremy Nicoll" <jn.ml.dbn.25@letterboxes.org> - 2020-10-07 12:00 +0200
    Re: Question: SSD speed Sven Hartge <sven@svenhartge.de> - 2020-10-07 12:50 +0200
      Re: Question: SSD speed Michael Stone <mstone@debian.org> - 2020-10-07 15:10 +0200
        Re: Question: SSD speed Andrei POPESCU <andreimpopescu@gmail.com> - 2020-10-08 11:00 +0200
          Re: Question: SSD speed "Thomas Schmitt" <scdbackup@gmx.net> - 2020-10-08 12:00 +0200
            [SOLVED] Re: Question: SSD speed Hans <hans.ullrich@loop.de> - 2020-10-08 12:20 +0200
            Re: Question: SSD speed Michael Stone <mstone@debian.org> - 2020-10-08 15:20 +0200
              Re: Question: SSD speed "Thomas Schmitt" <scdbackup@gmx.net> - 2020-10-08 16:00 +0200
                Re: Question: SSD speed Michael Stone <mstone@debian.org> - 2020-10-08 16:20 +0200
                Re: Question: SSD speed Stefan Monnier <monnier@iro.umontreal.ca> - 2020-10-08 17:40 +0200
                Re: Question: SSD speed Michael Stone <mstone@debian.org> - 2020-10-08 17:50 +0200
                Re: Question: SSD speed Stefan Monnier <monnier@iro.umontreal.ca> - 2020-10-08 18:00 +0200
              Re: Question: SSD speed Leslie Rhorer <lesrhorer@att.net> - 2020-10-08 20:30 +0200
                Re: Question: SSD speed Dan Ritter <dsr@randomstring.org> - 2020-10-08 20:40 +0200
                Re: Question: SSD speed Michael Stone <mstone@debian.org> - 2020-10-08 21:20 +0200
                Re: Question: SSD speed Leslie Rhorer <lesrhorer@att.net> - 2020-10-09 02:00 +0200
                Re: Question: SSD speed Michael Stone <mstone@debian.org> - 2020-10-09 02:20 +0200
                Re: Question: SSD speed Leslie Rhorer <lesrhorer@att.net> - 2020-10-09 02:40 +0200
                Re: Question: SSD speed Stefan Monnier <monnier@iro.umontreal.ca> - 2020-10-09 00:20 +0200
                Re: Question: SSD speed Leslie Rhorer <lesrhorer@att.net> - 2020-10-09 02:20 +0200
                Re: Question: SSD speed Stefan Monnier <monnier@iro.umontreal.ca> - 2020-10-09 15:50 +0200
    Re: Question: SSD speed Alberto Sentieri <22t@tripolho.com> - 2020-10-07 13:30 +0200
      Re: Question: SSD speed "Jeremy Nicoll" <jn.ml.dbn.25@letterboxes.org> - 2020-10-07 14:50 +0200
        Re: Question: SSD speed Andrei POPESCU <andreimpopescu@gmail.com> - 2020-10-08 10:50 +0200
    Re: Question: SSD speed Hans <hans.ullrich@loop.de> - 2020-10-07 18:50 +0200
      Re: Question: SSD speed "Jeremy Nicoll" <jn.ml.dbn.25@letterboxes.org> - 2020-10-07 18:50 +0200
      Re: Question: SSD speed Andy Smith <andy@strugglers.net> - 2020-10-07 19:50 +0200
        [SOLVED] Re: Question: SSD speed Hans <hans.ullrich@loop.de> - 2020-10-07 20:00 +0200
        [SOLVED] Re: Question: SSD speed Hans <hans.ullrich@loop.de> - 2020-10-08 09:10 +0200
  Re: Question: SSD speed Andrei POPESCU <andreimpopescu@gmail.com> - 2020-10-08 11:00 +0200

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