[PLUG] Confusion with DMA on or off

[Derek Loree]

On Wed, 2003-10-22 at 01:50, Sasha Romanosky wrote:
> I'm trying to confirm that DMA is enabled on two of my drives and I have
> conflicting output from boot up (dmesg) and hdparm. They are relatively
> new drives and I'm running mandrake 9.1. See below: 
> 
> root at fans[/var/log]# dmesg |egrep "hde|hdf"
>     ide2: BM-DMA at 0xdc00-0xdc07, BIOS settings: hde:DMA, hdf:DMA
> hde: MAXTOR 6L060J3, ATA DISK drive
> hdf: WDC WD1200BB-00DAA3, ATA DISK drive
> hde: DMA disabled
> hdf: DMA disabled
> hde: host protected area => 1
> hde: 117266688 sectors (60041 MB) w/1819KiB Cache, CHS=7299/255/63,
> UDMA(100)
> hdf: host protected area => 1
> hdf: 234441648 sectors (120034 MB) w/2048KiB Cache, CHS=14593/255/63,
> UDMA(100)

This last part looks like it is running UDMA, instead of DMA.  This is a
good thing, UDMA is a faster protocol.
> 
> 
> root at fans[/var/log]# hdparm /dev/hde
> /dev/hde:
>  multcount    = 16 (on)
>  IO_support   =  1 (32-bit)
>  unmaskirq    =  1 (on)
>  using_dma    =  1 (on)
>  keepsettings =  0 (off)
>  readonly     =  0 (off)
>  readahead    =  8 (on)
>  geometry     = 7299/255/63, sectors = 117266688, start = 0
> 
> root at fans[/var/log]# hdparm /dev/hdf
> /dev/hdf:
>  multcount    = 16 (on)
>  IO_support   =  1 (32-bit)
>  unmaskirq    =  1 (on)
>  using_dma    =  1 (on)
>  keepsettings =  0 (off)
>  readonly     =  0 (off)
>  readahead    =  8 (on)
>  geometry     = 14593/255/63, sectors = 234441648, start = 0
> 
> 
> I would tend to belive hdparm and if it is, indeed, correct, then I am
> puzzled by the "DMA disabled" from dmesg. Any ideas? 
> 
Try turning off DMA using hdparm, then rerun the -Tt tests.  They will
be slower if DMA was functioning before.

> cheers,
> sasha
> 
> 
> 
> fwiw, here's the output of hdparm -Tt on the two drives:
> root at fans[/etc/sysconfig/network-scripts]# hdparm -Tt /dev/hde
> 
> /dev/hde:
>  Timing buffer-cache reads:   128 MB in  1.48 seconds = 86.49 MB/sec
>  Timing buffered disk reads:  64 MB in  2.10 seconds = 30.48 MB/sec
> root at fans[/etc/sysconfig/network-scripts]# hdparm -Tt /dev/hde
> 
> /dev/hde:
>  Timing buffer-cache reads:   128 MB in  1.19 seconds =107.56 MB/sec
>  Timing buffered disk reads:  64 MB in  1.78 seconds = 35.96 MB/sec
> root at fans[/etc/sysconfig/network-scripts]# hdparm -Tt /dev/hde
> 
> /dev/hde:
>  Timing buffer-cache reads:   128 MB in  1.35 seconds = 94.81 MB/sec
>  Timing buffered disk reads:  64 MB in  2.02 seconds = 31.68 MB/sec
> root at fans[/etc/sysconfig/network-scripts]# hdparm -Tt /dev/hdf
> 
100 MB/sec. is about right for UDMA(100), the 30 MB/sec is about right
for a modern IDE drive.

> /dev/hdf:
>  Timing buffer-cache reads:   128 MB in  1.20 seconds =106.67 MB/sec
>  Timing buffered disk reads:  64 MB in  1.55 seconds = 41.29 MB/sec
> root at fans[/etc/sysconfig/network-scripts]# hdparm -Tt /dev/hdf
> 
> /dev/hdf:
>  Timing buffer-cache reads:   128 MB in  1.13 seconds =113.27 MB/sec
>  Timing buffered disk reads:  64 MB in  1.56 seconds = 41.03 MB/sec
> root at fans[/etc/sysconfig/network-scripts]# hdparm -Tt /dev/hdf
> 
> /dev/hdf:
>  Timing buffer-cache reads:   128 MB in  1.16 seconds =110.34 MB/sec
>  Timing buffered disk reads:  64 MB in  1.47 seconds = 43.54 MB/sec
> 
WOW, better than 40 MB/sec.  What kind of drive is that one?

HTH,

Derek Loree