On Tuesday, September 25, 2001 02:54:58 PM +0200 Jorge Nerín
<[EMAIL PROTECTED]> wrote:
>>
> Who says test.zero is a linear file and it's not scattered around the
> whole disk and the fs layer is filling holes...? If it's the case the
> write cache is a BIG win, just think that the fs writes a chunk at the
> beggining of the disk, then another chunk at the end, then another near
> the beginning, then... you get the picture, in this case the disk
> reorders the seeks to best fit.
>
> If you want to try a REAL linear write do a dd if=/dev/zero of=/dev/hde7
> or whatever unused partition you have.
>
Exactly, especially since during the dd you're going to seek back to the
log for a few commit writes.
>From a filesystem point of view, I've spent hours and hours getting
reiserfs to order the writes correctly to keep data consistent after a
crash. Turning on writeback caching without a battery backup more or less
throws all that work out the window. Don't do it.
For some people, a UPS counts as a battery backup, but there are lots of
reasons that doesn't fly in any kind of production environment. If your
job somehow depends on the data being safe, just get a raid controller with
batter backed cache.
-chris
