On Mon, 8 May 2000, Jeff Macdonald wrote:
> I read somewhere that putting a disk on the same ide cable as a CD-ROM
> slows the disk to the speed of the CD-ROM. Is this true? I only plan on
> using that disk for backup purposes, but I was just wondering if any one
> had some words of wisdom.
ATA (AKA IDE) has a number of performance issues. The biggest is that it
doesn't support disconnection: When one device (e.g., CD-ROM) is busy seeking,
the other (e.g., hard disk) is not accessible. This can significantly slow
things down if both the CD-ROM and an active filesystem are on the same IDE
chain.
Plain ATA is/was also a performance dog in general; as it used PIO
(programmed I/O) to transfer data one word at a time, rather then using DMA
(direct memory access). Newer ATA specifications attempt to introduce DMA
support, with varying degrees of success. Various interactions between
controllers, devices, OS, drivers, and the features they support mean that
putting a DMA device on the same chain as a non-DMA device may force them both
into non-DMA mode.
So, the short answer is: Try to keep things like CD-ROMs and Zip drives off
of the IDE bus(es) your active hard disk(s) are on. However, a disk used
mainly for archive purposes should be fine.
> After I recover, I think I will send a patch to the 'dd' maintainers. The
> patch would ask 'Do you really want to overwrite that device? (Yes/No)' by
> default, and have a 'don't ask' option for batch programs.
Problem is, that would break an *awful* lot of existing software.
You might be able to add a "-i" switch to dd(1), similar to rm(1), and use
shell aliases to make it the default.
--
Ben Scott <[EMAIL PROTECTED]>
| "Meddle not in the affairs of wizards, for they are subtle, and quick |
| to anger." -- J.R.R. Tolkien |
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