buffer size on HDs does size matter?

Discussion in 'PC Hardware' started by Pdigmking, Dec 4, 2005.

  1. Pdigmking

    Pdigmking Guest

    Been looking at HDs as of late. I see that Samsung has 2MB buffers while
    almost everyone else has 8. I read a little hard drive explanation thing
    that suggested that the manufacturers are adding buffer size because it's
    cheap, but it doesn really add that much to performance?

    Any comments?

    Paul.
     
    Pdigmking, Dec 4, 2005
    #1
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  2. Pdigmking

    dawg Guest

    New drives are coming out with 16MB. It makes a small difference. From 2mb
    to 8mb or 16mb is a noticeable difference. From 8 to 16 not much.
     
    dawg, Dec 4, 2005
    #2
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  3. Pdigmking

    Rod Speed Guest

    That is just plain wrong, they have both.

    Yep, you wouldnt be able to pick the drive with
    the bigger cache without using a benchmark.
    Basically because 2MB is plenty.
    More that its pointless.
    Nope, it has minimal effect on performance.
    Because that's fine.
     
    Rod Speed, Dec 5, 2005
    #3
  4. Pdigmking

    Arno Wagner Guest

    I think the problem is that in order to really speed up reading,
    you would need more like 256MB and more of cache. What the small
    sizes are good for is speeding up writes by buffering them. But
    if you make these buffers too large, you might loose data if people
    shut down their computer but the disk has not finished writing
    when the power goes off.

    Maybe the disk manufacturers do benchmarks with Windows on how
    much time they have between the last write and the poweroff and
    design buffer size accordingly...

    The other possible reason is that it is SRAM, not DRAM as in
    computer memory, and SRAM is more expensive.

    Arno
     
    Arno Wagner, Dec 5, 2005
    #4
  5. Pdigmking

    Conor Guest

    The idea of a buffer is twofold.

    1) Cache frequently accessed files.
    2) Hold data in fastest storage to make it immediately available to the
    interface when the IDE/SATA port requests it.
     
    Conor, Dec 5, 2005
    #5
  6. Pdigmking

    Rod Speed Guest

    Not with the buffer on the hard drive, thats done by the OS cache.
    Its mostly used to buffer writes with hard drives.
     
    Rod Speed, Dec 5, 2005
    #6
  7. A number plucked from your arse?
    Hardly.
    Even if the full cache were to be used it only gives a .1 second advantage.
    Maybe if the drive is badly fragmented it may get slightly more noticeable.
    We are talking cache here, not (just) buffer.
    The 'cache' is divided in read cache, write cache and buffer.
    Caches are divided in segments of which only a percentage is used
    to buffer (read ahead, write behind), apart from the 'buffer', that is
    only 128kB and buffers only a single command, whether read or write.
    The rest is used to keep earlier instances of reads and writes and they
    will be overwritten in time, usually oldest data first.
    So obviously you are not talking about the cache as a whole.
    Or it is just single chip memory that is differently organized than
    computer memory and therefor not produced in the same quantity
    as computer memory and consequently more expensive.
     
    Folkert Rienstra, Dec 5, 2005
    #7
  8. Pdigmking

    Joe Yong Guest

    Not really.

    HDD buffers are mostly to cache writes. Caching reads are done by the
    application, OS or controller. Moving read caching to the drive is possible
    but involves quite a lot more than plugging a few ICs into the board. Read
    aching is not rocket science, conceptually, but implemeting it efficiently
    and to yield positive impact is almost rocket science.


    joe.
     
    Joe Yong, Dec 5, 2005
    #8
  9. Pdigmking

    Rod Speed Guest

    Particularly when done at the drive level when the drive
    only knows about logical blocks and not about files etc.

    Makes a lot more sense to do that sort
    of caching at the OS level or the app level.
     
    Rod Speed, Dec 5, 2005
    #9
  10. Pdigmking

    Pdigmking Guest

    @individual.net:

    So Rod,

    Your saying that 8MB doesn't really improve performance over 2MB?

    By the way, I was referring to certain Samsung IDE drives which are now
    only available with 2MB buffer, I realize that Samsung has drives with 8MB,
    but he question remains.. 2 vs. 8?

    Paul
     
    Pdigmking, Dec 5, 2005
    #10
  11. Pdigmking

    JAD Guest

    Do you stare at Benchmarks? Then forget it, you'll never 'see' the
    difference.
     
    JAD, Dec 5, 2005
    #11
  12. Pdigmking

    Rod Speed Guest

    Nope, that the improvement in performance is quite small and 32MB
    will make very little difference at all since its basically a write buffer.
    Like I said, the difference is quite small.
     
    Rod Speed, Dec 5, 2005
    #12
  13. Apparently it is to you, judging by your post.
    That's saying the same thing twice, more or less:
    Caching "frequently accessed files" is "holding data in fastest storage to make it
    immediately available to the interface when the IDE/SATA port requests it".

    Presumably the second point is about caching ahead where a follow-up request
    to a previous request for parts of a sequential file is cached even before the
    followup request is issued and when it is issued the data comes from cache rather
    than from the platters.

    And then there is 3) and 4) as well, for the write cache side of the cache.

    Let's see those headers again, John Troll.
     
    Folkert Rienstra, Dec 5, 2005
    #13
  14. It doesn't need to know about files.
    A file is represented by block numbers and if a particular file is
    requested it is requested by those blocknumbers. If those blocknumbers
    happen to be available in cache, then that is where they will come from.

    Read-ahead caching is not about pre-emptive file caching, it is about caching
    sectors that are likely to be read next by the next IO but which IO may not
    arrive in time so that when it eventually does the data is available without
    having to wait a revolution to still pick that data up.
    Both don't know about your files either.
    All they can do is load files that are adjacent to the file that you are loading
    but that does nothing for the file that you are loading and the files that are
    adjacent to the file that you are loading may have nothing whatsoever to do
    with the app that you are using.
     
    Folkert Rienstra, Dec 5, 2005
    #14
  15. Pdigmking

    DaveW Guest

    Yes, the buffer size makes a noticeable difference in how fast the system
    can recall recent data from the harddrive. The 2 MB harddrives are old and
    out of date.
     
    DaveW, Dec 6, 2005
    #15
  16. Pdigmking

    JAD Guest

    prove it without a benchmark

     
    JAD, Dec 6, 2005
    #16
  17. Prove your dick is bigger than 4" without a benchmark?
    Aha!! That explains sooo much!

    *sigh*

    Luddites are so boring.
     
    Michael Cecil, Dec 6, 2005
    #17
  18. Pdigmking

    JAD Guest

    Yes it does....about you
     
    JAD, Dec 6, 2005
    #18
  19. Pdigmking

    Rod Speed Guest

    Wrong when deciding what to cache. Most obviously with
    caching directory structures in preference to files etc.
    Irrelevant to deciding what its more important to cache.
    It was caching in general that was being
    discussed, not just read ahead caching.
    See above.
    Wrong again.
    Wrong again.
    Never said it did.
    Never said they did.

    The OS can obviously distinguish between directory structures
    that are more likely to be used again and files loaded by apps,
    can know what processes requested which files and which
    processes are no longer running and so are less likely to
    request that file again, etc etc etc.

    In spades with the apps where decent database apps can be
    a lot more intelligent about what data they cache internally etc.

    Thanks for that completely superfluous proof that you have never
    ever had a fucking clue about anything at all and couldnt manage
    a viable troll if your pathetic excuse for a 'life' depended on it.
     
    Rod Speed, Dec 6, 2005
    #19
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