[linux-lvm] Performance problem.

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Mon Nov 17 12:45:02 UTC 2003

>>   No,  that  is  true.  Your low read speed does indicate that you are
>>   not  using  DMA.  Give  us  the  output of "hdparm /dev/hda". Also a
>>   simple  benchmark is to do "dd_rescue /dev/hda /dev/null". What does
>>   that give you in numbers?

> /dev/hdd:
>  multcount    = 16 (on)
>  IO_support   =  1 (32-bit)
>  unmaskirq    =  0 (off)
>  using_dma    =  1 (on)
>  keepsettings =  0 (off)
>  readonly     =  0 (off)
>  readahead    =  8 (on)
>  geometry     = 14589/255/63, sectors = 234375000, start = 0

  This  looks good. You could try -c3 to enable 32-bit w/sync and also
  enable  Write  cache  -W1 (this may and many not be wise in case you
  have power failures often).

> the cables are new (I thought that they may be a problem), I've
> gotten far better speeds on the same system and a worse system
> before I used lvm on the same drives.  I REALLY doubt there's
> something wrong with the drives (I replaced one of them because of
> an error, and looked for trouble after replacing that one, but
> didn't find anything else).

> And that dd_rescue will read from /dev/hda and write to /dev/null
> right?  Meaning it's a read test, and not a write test (= I won't
> loose any data on it ;) ).

  Yes,  it  is a read-only test! Read the manpage to get all flags you
  can use with it (such as how big blocks it is to read etc).

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