PIO versus UDMA

[\One Punch\ Mickey]

We inherited a customer who has a single P4 1GHz server with 512MB RAM
containing two hard drives, not mirrored or RAID. Both drives are
running in PIO mode for some reason and the customer is continually
complaining of speed problems. I can't find any comparative benchmarks
between PIO and UDMA to show them - are there any around?

 

[Arno Wagner]

We inherited a customer who has a single P4 1GHz server with 512MB RAM
containing two hard drives, not mirrored or RAID. Both drives are
running in PIO mode for some reason and the customer is continually
complaining of speed problems. I can't find any comparative benchmarks
between PIO and UDMA to show them - are there any around?

Not that I know. But the disk I/O speed can be slower by a factor of
10 or more with PIO in comparison to DMA. At least that is my
observation with Linux and ext2/3.

Arno

 

[\One Punch\ Mickey]

Thanks Arno.

 

[Folkert Rienstra]

We inherited a customer who has a single P4 1GHz server with 512MB RAM
containing two hard drives, not mirrored or RAID. Both drives are
running in PIO mode for some reason and the customer is continually
complaining of speed problems. I can't find any comparative benchmarks
between PIO and UDMA to show them - are there any around?

From the ATA spec: www.t13.org

"
The ATA bus is a storage interface originally designed for the ISA Bus
of the IBM PC/AT. With the advent of faster host systems and devices,
the definition of the bus has been expanded to include new operating
modes. Each of the PIO modes, numbered zero through four, is faster
than the one before (higher numbers translate to faster transfer rates).

PIO modes 0, 1, and 2 correspond to transfer rates for the interface as was
originally defined with maximum transfer rates of 3.3, 5.2, and 8.3 megaby-
tes per second (MB/s), respectively. PIO mode 3 defines a maximum transfer
rate of 11.1 MB/s, and PIO mode 4 defines a maximum rate of 16.7 MB/s.

Additionally, Multiword DMA and Ultra DMA modes have been defined.
Multiword DMA mode 0, 1, and 2 have maximum transfer rates of 4.2,
13.3, and 16.7 MB/s, respectively.

Ultra DMA modes 0, 1, 2, 3, 4, 5 and 6 have maximum transfer rates
of 16.7, 25, 33.3, 44.4, 66.7, 100 and 133 MB/s, respectively.
"

Note that these are busspeeds (MHz) converted into MB/s and include
protocol and command overhead. Actual user data transfer speeds are lower.
Deduct 10% for DMA, more for PIO.

 

[Cl.Massé]

We inherited a customer who has a single P4 1GHz server with 512MB RAM
containing two hard drives, not mirrored or RAID. Both drives are
running in PIO mode for some reason and the customer is continually
complaining of speed problems. I can't find any comparative benchmarks
between PIO and UDMA to show them - are there any around?

PIO is slower because it involves the intervention of the processor. The
operating system may downgrade from UDMA to PIO because of disk errors. The
solution is to uninstall the disk driver, to set to UDMA, and to reboot (at
least in Windoze XP.)

 

[Arno Wagner]

""One Punch" Mickey" <[email protected]> a écrit dans le message de [email protected]

PIO is slower because it involves the intervention of the processor. The
operating system may downgrade from UDMA to PIO because of disk errors. The
solution is to uninstall the disk driver, to set to UDMA, and to reboot (at
least in Windoze XP.)

Actually the permanent solution is to first get rid of the
disk-interface errors. Otherwise you will just see the speed
downgraded again.

Then your OS may or may not require attention to resume using
DMA. In Linux a reboot is sufficient for that.

Arno