# slow reading from drive

## zerkms

hello

i have 2 single drives (sdb - 1tb, sdc - 750gb)

and reading from sdb is slow (about 10mbytes/sec). so when i copy from sdb to sdc or to network - i get 10mb/s

and when writing to sdb from sdc or from network - i get about 50mb

it's correct udma specified:

UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5 *udma6

any ideas?

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## zerkms

following to https://forums.gentoo.org/viewtopic-p-5965360.html?sid=ce8604fdaaf1a8de39afb0d68df3b34e - i have fragmentation issue... so, what is the better solution then? (the current filesystem is ext3)

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## NeddySeagoon

zerkms,

I can't really account for the asymetric read/write speeds.

Soem things to check are :-

In the BIOS, you are not using IDE mode or Compatibility Mode. That often turns off DMA.

Try a new data cable, or even just disconnecting and reconnecting the data cable (both ends).

A data transfer problems lead to retries, which means the data is resent. The overall effect is to reduce the data rate.

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## zerkms

 *NeddySeagoon wrote:*   

> zerkms,
> 
> I can't really account for the asymetric read/write speeds.
> 
> Soem things to check are :-
> ...

 

if some bios settings were wrong the second drive would be slow too, i think...

now i'm deleting unneeded stuff from sdb and will try to split sdb into 2 partitions, small for torrents (which caused fragmentation) and big for storage.

if the same trouble will be - then i will try to think something else (as of changing cable) - because that pc is in place hard to reach now %)

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## eccerr0r

Are the numbers you're getting from hdparm is it from reading/writing using cp, or something?

My guess is that if you're reading from a heavily fragmented file you can get really poor read speeds, BUT if you write to an unfragmented portion of your hard drive, then speeds are very fast...  But then supposedly reading from this unfragmented file it should be fast as well.

Definitely try to defragment.  It now seems a lot of torrent applications, to make your hard drive space "look" good while it's downloading it will create sparse files, and unfortunately I think most filesystems get confused when creating sparse files when avoiding fragmentation.  

Technically it should allocate the space and treat it as if the space was allocated but resist putting stuff in those extents... which is still not optimal when your disk is about full... can't avoid fragmentation there.  Only realy way is to just preallocate the file completely with zeroes -- that will avoid fragmentation entirely but cost hash check times in case of stopped downloads, and you have to have all the space there up front.

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