[fdutils] Re: creating high-capacity disks without --verify_later does not work

Alain Knaff alain.knaff at lll.lu
Sat Nov 2 21:28:10 CET 2002


On Sunday 30 June 2002 14:43, Jochen Voss wrote:
> It seems, that the verify code uses the _old_ drive
> parameters (either whatever was autodetected for media
> that was in the drive before, set with setfdprm, or the
> default) to verify the tracks, which are formatted with
> the new parameters.
[...]
>     voss at automatix [~] superformat /dev/fd0 ds hd sect=21
>
> This command results in a lot of I/O errors
> and noises like the floppy drive is suffering.
> The first few error messages are

I checked it out: the floppy parameters look correct; however there is
something else going on:

In recent kernels, the generic VFS's layer's read-ahead behavior has
changed. Now, the VFS attempts to read ahead on floppies, even if
BLKRA is set to 0.

In its default config, superformat alternatively formats a track, and
then immediately attempts to read from it (by using the system's read
syscall, rather than using raw floppy I/O). The problem is that then
the VFS decides to read ahead, and stumbles accross tracks which are
_not_yet_ formatted at that time, hence the scary noises.

Even when reformatting a disk as the same format, noises occur,
because reads and formatting now happen "in parallel", forcing the rw
head to move in an erratic pattern.

> If I try the same with the "--verify_later" option,
> everything works fine:

Exaclty.

In today's patch, I made --verify_later the default.

In order to get the old behavior back, use --verify_later=0

Regards,

Alain

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