Re: RAID on laptop or xfs?

On Thu, 31 Mar 2005, Russell Howe uttered the following:
> Even worse, some drives *IGNORE* a request to disable write caching! In
> this case, there isn't a whole lot the filesystem can do other than take
> a guess at the state of the drive (although I think I read something on
> the linux-xfs list talking about cache barriers or something...).

A lost cause, if you ask me: if a drive's so loony nonstandard as to
ignore cache disable requests, why on earth would it respect the (much
less frequently implemented) cache barrier ops?

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Re: debian kernel 2.6.11 syslog erros

On Thu, 31 Mar 2005, t. clarke yowled:
> Finally think I cracked the syslog problem
> It seems there is a kernel parameter for 'event logging' with the serial driver
> section. I disabled it and the problem seems to have gone away.

This is a feature, not a bug. The point of evbug.c is to log
*everything* that flows through the event layer.

I've found it useful in the past to localize keyboard problems to X or
to the hardware, respectively. (The downside of using a weird keyboard:
the occasional odd firmware bug and implementation of the keyboard spec
in valid ways which X misinterprets...)

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Re: OT: New arrival & status of open source in the UK.

Hi

Well in South Africa it's not doing as well as we would like, of
course we would not be satisfied no matter what.<g>

There is a daytime program on Saturday's called Go-Open which is
sponsered by TSF, the CSIR, HP, etc and it is having an impact, I've
had people who run windows only shops asking me about it. It was great
fun pulling out an Ubuntu CD pack and handing it to the business owner
who asked me about it.<g>

There is a bIg push into schools with computer labs of refurbished
computers in a thin client configuration - gratis (another TSF
project). Microsoft responded absolutely perfectly IMO by offering
free software to schools - they send them a pack of software with
corporate install media and licences after they complete and send off
an application form.

Impi linux has been largely eclipsed by Ubuntu linux but Cubit is
starting to gain ground as an accounting solution. Very impressive and
useful in that you can run it as a web based server & client access
system and be completely cross-platform.

The freedom toaster project is starting to take off now (i.e. many
more toasters are now ready and are being shipped around the country).
Here you can rock up with blank CD' s or purchase them from a
neighbouring vending machine and burn 1 or more of the 12 or so linux
distro's on the toaster. This was very popular at the last Futurex
conference in Cape Town. It's also burned many distro's at it's
permanent home at the MTN science centre.

Re: RAID on laptop or xfs?

Yup drives do tend to do perform lots of black magic behind the ATA
interface, not a lot you can do about that except make sure it won' t
cause problems.

Buy a UPS? That's what we'd do back home. <g>

I'm not sure how much hdd corruption you will suffer if you are using
a journalling file system when the drive loses power, all changes to
files being stored in the journal.

If some of that cache is for reads (i.e. not stuff waiting to be
written) than you can ignore that for data corruption purposes.
Combining these two factors means you should survive. Of course if you
can' t take that kind of a risk then you should be using high end
controllers with battery backed cache and have everything on a UPS.

Regards
Liam     

On Fri, 01 Apr 2005 00:52:28 +0100, Nix <nix <at> esperi.org.uk> wrote:
> On Thu, 31 Mar 2005, Russell Howe uttered the following:
> > Even worse, some drives *IGNORE* a request to disable write caching! In
> > this case, there isn't a whole lot the filesystem can do other than take
> > a guess at the state of the drive (although I think I read something on
> > the linux-xfs list talking about cache barriers or something...).
> 
> A lost cause, if you ask me: if a drive's so loony nonstandard as to
> ignore cache disable requests, why on earth would it respect the (much
> less frequently implemented) cache barrier ops?
> 

Re: Re: RAID on laptop or xfs?

On Fri, Apr 01, 2005 at 01:33:44AM +0100, Liam wrote:
> 
> I'm not sure how much hdd corruption you will suffer if you are using
> a journalling file system when the drive loses power, all changes to
> files being stored in the journal.

Except that they will not all be there if some of the changes were in
the writeback cache, that's the whole problem.  What makes it worse is
that these drives do not usually flush the data blocks from the cache to
the disk in the same order that they were written to it.  This can make
complete nonsense of a journal or mean that only random portions of a
RAID stripe were written to disk at poweroff.

> 
> If some of that cache is for reads (i.e. not stuff waiting to be
> written) than you can ignore that for data corruption purposes.

It's called a writeback cache.

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Re: debian kernel 2.6.11 syslog erros

Nix
Thanks for the further info re event logging feature
Possibly ithe keyboard I am using on this machine (grabbed from the spares shelf
) is iffy.   I will renable the dfeature and try another keyboard.

TIm
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Copier offer

Hello,
   I have just been offered a working copier complete with spare toners,
etc, but it comes with a few minor difficulties.

1  I was told that it will cost a few drinks

2  it must be collected from a ground floor doorway with good vehicle access
close to the A40 Western Avenue, Park Royal

3  it is about the biggest copier available, and will need a lorry with tail
lift (I think it is a Canon monochrome with auto feed and every possible
extra tray, sorting and collating facility, etc) Reason for offer: too big.

   If anyone, especially a worthy cause or charity, has a genuine use for it
please let me know ASAP and I will check if it is still available.

--
Chris Bell

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Re: RAID on laptop or xfs?

Well that does sound painful. I've had problems with this sort of
thing but only before changing to ReiserFS (from EXT2) but then I also
aquired a UPS for the machine in question...

Of course a laptop has a battery so don't need a UPS, which is good
because the Lead / Acid batteries in UPS weigh a _lot_ .<g>

My understanding is that the integrity of the journal itself is not
that crucial fro the integrity of the filesystem because as soon as
the journal gets hosed by the drive losing power and the contents of
the cache dissapearing into the ether, the journal is no longer in a
postition to write its contents to the rest of the file system.

It could be interesting to see the effect that different cache sizes
(512K, 2MB, 8MB) and journal sizes have on the problem. Of course if
the drive is busy making the changes that the journal has stroed int
it to the rest of the FS atm the power is lost then there could well
be corruption, if the power loss also hoses the journal at the same
time then undoing any changes woudl be far more difficult.  Then it' s
time to say fsck it and / or reach for the backups.

cheers
Liam

On Fri, 1 Apr 2005 07:04:13 +0100, Bruce Richardson
<itsbruce <at> uklinux.net> wrote:
> On Fri, Apr 01, 2005 at 01:33:44AM +0100, Liam wrote:
> > 
> > I'm not sure how much hdd corruption you will suffer if you are using
> > a journalling file system when the drive loses power, all changes to

Re: debian kernel 2.6.11 syslog erros

On Fri, Apr 01, 2005 at 08:41:27AM +0100, t.clarke wrote:
> Nix
> Thanks for the further info re event logging feature
> Possibly ithe keyboard I am using on this machine (grabbed from the spares shelf
> ) is iffy.   I will renable the dfeature and try another keyboard.

Could you by any chance have enabled CONFIG_INPUT_EVBUG in the kernel
configuration without realising it?

CONFIG_INPUT_EVBUG:

Say Y here if you have a problem with the input subsystem and
want all events (keypresses, mouse movements), to be output to
the system log. While this is useful for debugging, it's also
a security threat - your keypresses include your passwords, of
course.

Symbol: INPUT_EVBUG [=n]
Prompt: Event debugging
  Defined at drivers/input/Kconfig:122
  Depends on: INPUT
  Location:
    -> Device Drivers
      -> Input device support

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Re: Re: RAID on laptop or xfs?

On Fri, 1 Apr 2005, Liam Smit yowled:
> My understanding is that the integrity of the journal itself is not
> that crucial fro the integrity of the filesystem because as soon as
> the journal gets hosed by the drive losing power and the contents of
> the cache dissapearing into the ether, the journal is no longer in a
> postition to write its contents to the rest of the file system.

But, er, when the system restarts and the journal is replayed, the
journal will be written to the FS. That's kind of the point. ;)

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