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Re: SSD drive reliability.

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"Charles T. Smith" <cts.private.yahoo@gmail.com> writes:

> On Mon, 16 Jun 2014 10:41:36 +0200, David Brown wrote:
>
>> On 14/06/14 09:50, Charles T. Smith wrote:
>>> On Tue, 10 Jun 2014 01:15:14 +0000, Bob Tennent wrote:
>>> 
>>>> On Tue, 10 Jun 2014 02:01:17 +0100, Måns Rullgård wrote:
>>>>  > Bob Tennent <BobT@cs.queensu.ca> writes:
>>>>  >
>>>>  >> On Tue, 10 Jun 2014 00:57:17 +0100, Måns Rullgård wrote:
>>>>  >>  >
>>>>  >>  >> SSDs in general are considered to be much more reliable than
>>>>  >>  >> HDs.
>>>>  >>  >
>>>>  >>  > When did this change?
>>>>  >>
>>>>  >>   "From the data I've seen, client SSD annual failure rates under
>>>>  >>   warranty tend to be around 1.5%, while HDDs are near 5%," Chien
>>>>  >>   said.
>>>>  >
>>>>  > How long is the warranty for each?  Does this statistic take into
>>>>  > account the vastly different capacities?
>>>>
>>>> The subject of SSD reliability is rather controversial. As I
>>>> suggested, Google "SSD reliabilty" for lots of discussion.
>>> 
>>> 
>>> What's the difference between an SSD and a flash usb stick?  I have
>>> tried repeatedly to use flash usb sticks as linux drives, using ext2 as
>>> the FS and mounted with the noatime option to avoid too many accesses. 
>>> After only a few mounts, these FS always end up corrupted.
>>> 
>>> The problem with flash is that "checking" them for integrity only
>>> decreases their lifetime.
>>> 
>>> I don't use flash anymore, for anything.
>>> 
>>> 
>> There is a world of difference between the average SSD and the average
>> flash stick (though less between the lowest of SSD's and the best of
>> flash sticks).
>> 
>> Flash sticks usually have minimal or no wear levelling, redundancy,
>> error checking, sector re-mapping, etc.  Instead of wear levelling, they
>> often have special flash for the first few MB's that supports many more
>> erase/write cycles - specifically to handle the extra pressure FAT
>> places on those sectors.  The rest of the flash is as cheap as possible,
>> as is the controller.
>> 
>> ext2 does not use a FAT - its high-use tables are in different areas of
>> the disk, thus you will wear out a USB flash stick faster with ext2 than
>> with FAT.
>> 
>> Flash sticks are also very prone to damage if you are not finished
>> writing before you remove them - always umount them (or at least "sync"
>> them) before unplugging.  It is not enough just to wait for the led (if
>> it has one) to go off.
>
> So, in conclusion - don't use an SSD if you're going to run linux.

Wrong conclusion.  USB flash sticks are sometimes (allegedly) optimised
for FAT, but SATA-attached SSDs are a different story entirely.

> As to wear-leveling ... that's presumably in the OS driver.  Maybe.  I 
> wonder if any drivers report statistics.

Wear levelling is done entirely by the SSD controller.  The exact
implementations are closely guarded secrets of each manufacturer, but
broadly speaking, it works by continuously remapping logical sectors
(used in SATA commands) to different physical locations in the flash
memory.  Even sectors that are not explicitly written might be relocated
at times.  To aid the wear levelling process, SSDs support a "trim"
command which allows the OS to tell the drive when sectors no longer
hold useful data, e.g. after deleting a file.  Like HDDs, SSDs support
SMART for reporting various attributes related to the health of the
drive.

> I mean, the very concept of load leveling says everything that needs to 
> be said.  What happens to those areas which get reduced usage?  It 
> presumably means they've been worn - maybe they still work, but do you 
> ever want to use them again?  Which access is going to be the one that 
> tips them?
>
> Is flash/SDD a fancy WORM drive?

No.

-- 
Måns Rullgård
mans@mansr.com

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Thread

SSD drive reliability. wexfordpress <john@wexfordpress.com> - 2014-06-09 15:49 -0700
  Re: SSD drive reliability. Bob Tennent <BobT@cs.queensu.ca> - 2014-06-09 23:13 +0000
    Re: SSD drive reliability. Måns Rullgård <mans@mansr.com> - 2014-06-10 00:57 +0100
      Re: SSD drive reliability. Bob Tennent <BobT@cs.queensu.ca> - 2014-06-10 00:54 +0000
        Re: SSD drive reliability. Måns Rullgård <mans@mansr.com> - 2014-06-10 02:01 +0100
          Re: SSD drive reliability. Bob Tennent <BobT@cs.queensu.ca> - 2014-06-10 01:15 +0000
            Re: SSD drive reliability. "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2014-06-14 07:50 +0000
              Re: SSD drive reliability. Poutnik <poutnik@privacy.net> - 2014-06-14 10:19 +0200
              Re: SSD drive reliability. "Trevor Hemsley" <Trevor.Hemsley@mytrousers.ntlworld.com> - 2014-06-14 21:10 -0500
                Re: SSD drive reliability. "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2014-06-15 08:48 +0000
              Re: SSD drive reliability. David Brown <david.brown@hesbynett.no> - 2014-06-16 10:41 +0200
                Re: SSD drive reliability. "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2014-06-17 10:24 +0000
                Re: SSD drive reliability. Måns Rullgård <mans@mansr.com> - 2014-06-17 12:24 +0100
                Re: SSD drive reliability. Richard Kettlewell <rjk@greenend.org.uk> - 2014-06-17 12:44 +0100
                Re: SSD drive reliability. David Brown <david.brown@hesbynett.no> - 2014-06-17 14:43 +0200
                Re: SSD drive reliability. "David W. Hodgins" <dwhodgins@nomail.afraid.org> - 2014-06-17 12:34 -0400
                Re: SSD drive reliability. David Brown <david.brown@hesbynett.no> - 2014-06-18 10:06 +0200
                Re: SSD drive reliability. "David W. Hodgins" <dwhodgins@nomail.afraid.org> - 2014-06-19 16:29 -0400
                Re: SSD drive reliability. Fredrik Jonson <fredrik@jonson.org> - 2014-08-13 09:15 +0000
                Re: SSD drive reliability. David Brown <david.brown@hesbynett.no> - 2014-08-13 13:09 +0200
                Re: SSD drive reliability. Richard Kettlewell <rjk@greenend.org.uk> - 2014-08-13 12:59 +0100
                Re: SSD drive reliability. David Brown <david.brown@hesbynett.no> - 2014-08-13 15:52 +0200
      Re: SSD drive reliability. JEDIDIAH <jedi@nomad.mishnet> - 2014-06-09 19:45 -0500
        Re: SSD drive reliability. David Brown <david.brown@hesbynett.no> - 2014-06-10 08:51 +0200
  Re: SSD drive reliability. "Vince Coen" <VBCoen@gmail.com> - 2014-06-10 11:49 +0100

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