I get the feeling that my hard disk is very slow. Is there a way I can verify and tune it?

You can use hdparm to tune your hard disk. On Debian, you would run

apt-get install hdparm

to install it.

hdparm --help

shows a list of all available options. To get more information about your hard disk, run

hdparm -i /dev/hda

This will look like:

/dev/hda:

Model=MAXTOR 6L060J3, FwRev=A93.0500, SerialNo=663214759549
Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs }
RawCHS=16383/16/63, TrkSize=32256, SectSize=21298, ECCbytes=4
BuffType=DualPortCache, BuffSize=1819kB, MaxMultSect=16, MultSect=16
CurCHS=4047/16/255, CurSects=16511760, LBA=yes, LBAsects=117266688
IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
PIO modes:  pio0 pio1 pio2 pio3 pio4
DMA modes:  mdma0 mdma1 mdma2
UDMA modes: udma0 udma1 *udma2
AdvancedPM=no WriteCache=enabled
Drive conforms to: ATA/ATAPI-5 T13 1321D revision 1:

* signifies the current active mode

To see how fast your hard disk currently is execute

hdparm -tT /dev/hda

The output:

/dev/hda:
Timing cached reads:   972 MB in  2.00 seconds = 486.00 MB/sec
Timing buffered disk reads:   72 MB in  3.08 seconds =  23.38 MB/sec

Now you can run

hdparm -c1 -d1 -X 66 /dev/hda

to tune your hard disk. The X flag stands for the transfer mode (PIO: 8; DMA: 32; U-DMA: 64) + the number of the mode (2 for udma2: 64 + 2 = 66).

Now run

hdparm -tT /dev/hda

again, and if you're lucky, your hard disk should have become "faster".