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Groups > comp.os.linux.hardware > #2431

Re: SSD drive reliability.

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On 17/06/14 12:24, Charles T. Smith wrote:
> 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.

No - I have no idea how you could come up with that after reading my post.

The conclusion is that flash sticks have limited lifetimes no matter
what system, and will probably have problems faster with ext2 than with
FAT.  Flash sticks are usually very cheap, and you get the quality you
pay for.  But they are still perfectly usable with Linux (and Windows,
Macs, tablets, etc.), as long as you don't assume they will be reliable
for heavy usage over time.  There is also no requirement to use ext2 for
Linux - since flash sticks are often used to transfer data between
machines, it is very common to stick to FAT even if the main platform is
Linux.

And as I said, SSD's are a completely different thing.  A decent SSD is
going to be more reliable, and have a longer expected lifetime than a
harddisk.  It will also give better results with Linux than it would
with Windows (simply because the disk system and the filesystems are
better in Linux, and you can be more intelligent about trimming in Linux).

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

No, it is not part of the OS driver - it is part of the firmware of the
device.  You will probably not be able to get much in the way of
statistics, as that will be internal to the drive.  But don't worry
about it - if you buy a good quality SSD (it does not need to be top of
the range) then you can usually write continuously at speeds of 30+ MB
every second for /years/ before wearing out the flash.

> 
> 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?

Wear levelling is about spreading the erase/write loads across the flash
blocks, because flash blocks gradually deteriorate after between 1000 to
100000 erase/write cycles (depending on the type of flash).  The
deterioration is gradual, so the SSD firmware sees it is happening and
avoids re-writing a block that is becoming a problem long before it gets
unusable.  A good SSD will also move unchanging data around
occasionally, to make better use of blocks that are rarely written (this
is something that flash sticks, and old or cheapo SSDs usually do not
do).  So you can happily re-write the same logical block millions of
times, and the SSD firmware will spread it out across all blocks to give
an even wear.

> 
> Is flash/SDD a fancy WORM drive?
> 

No.

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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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