Re: [PATCH] 2.4.10 improved reiserfs a lot, but could still be better

[Nicholas Knight]

On Tuesday 25 September 2001 03:42 am, Matthias Andree wrote:
> On Mon, 24 Sep 2001, Nicholas Knight wrote:
> > It's a very remote possability of failure, like most instances
> > where write-cache would cause problems. Catastrophic failure of the
> > IDE cable in mid-write will cause problems. If write cache is
> > enabled, the write stands a higher chance of having made it to the
> > drive before the cable died, with it off, it stands a higher chance
> > of NOT having made it entirely to the drive.
>
> Cables don't suddenly die without the help of e. g. your CPU fan.

I explained in another message the situation I was thinking of, 
accidental pulling of the cable.

>
> > For most drives, I don't know for sure if they'd finish the write
> > that's now sitting in their cache, but I expect higher quality
> > drives (such as our IBM drives) definitely would. Infact I may even
> > be willing to test this later (my swap partition looks like it
> > wants to help :)
>
> Drives would not write incomplete blocks.

Not what I ment, I ment that if a write gets to the drive completely, 
and part is still sitting in the cache, I'd think the drive would 
continue to write it out as long as it has power. I wasn't reffering to 
the write partialy being down the cable.

> >
> > Either Maxtor or Western Digital share very close designs to IBM
> > drives, I belive they had some sort of development partnership. I'm
> > not sure if it was Maxtor or WD.
>
> The Western Digital 420400D (20 GB, 5400/min) and its 7200/min
> brother with 18 GBs were IBM disk drives, supposedly, but the WD
> ...AA/BB drives and whatever else there was looked some different
> from IBM drives.
>
> > > Why are disk drives slower with their caches disabled on LINEAR
> > > writes?
> >
> > Maybe the cache isn't doing what we think it is?
>
> Maybe. A monitor software or debug mode would be good to see when
> writes are scheduled and which blocks are written (I need to ask a
> friend of mine who hacked ll_rw_blk.c on a different purpose for his
> diploma thesis, maybe his code is valuable to figure things out.)
>
> > Does anyone have contacts at IBM and/or Western Digital?
> > Something's up... The 256MB write with write-cache off was going at
> > 5.8MB/sec, and with it on it was going at 14.22MB/sec (averages).
> > One interesting thing, the timings are showing a pretty consistant
> > but tiny increase in sys time with write caching on.
>
> I also saw that here, but again, it's basically the same hardware.