Hi!
Is there anybody out there who knows how QNX’s (4.24) file system behaves
when the system are shot down in a non controlled way, i.e loss of power?
/Ivar
Ivar Nilsson <ivar.nilsson@traffic.combitech.se> wrote:
Hi!
Is there anybody out there who knows how QNX’s (4.24) file system behaves
when the system are shot down in a non controlled way, i.e loss of power?
Well when you loose power, Fsys ceases to exist, so what is
important is what Fsys does before your shut down the power.
There are two issues to mention.
First is integrity and meta-data. Meta data is those structures
on the hard disk that are not your data itself. This includes
directory structures, inodes, and the .bitmap file data. Under
normal circumstances, QNX gives meta data the highest priority
to the disk. This is so that if you have an uncontrolled power
down, in most circumstance the structure of the disk will
be sound. You may turn this feature off in a number of ways.
One is to give Fsys the -a option. The other is to use the
-a option when mounting a disk. Note that the floppy driver
does not use this feature as the default.
The second issue is delay. The Fsys -d option controls
the delay between the time a write cache buffer is
received by Fsys, and when it is scheduled to be
written to disk. In all circumstances this is a
relatively short period, three seconds, but you
can shorten it if you like. The default provides
a good compromise between system integrity and
performance.
There are other ways to control how quickly blocks
are put on disk at an application level.
So in general, the structure of the file system
remains intact. Exceptions would be if you are
doing a lot of meta data updates, such as when
you are loading a bunch of small files. Using
the -a option will also make the disk structure
more vulnerable during updates. When in doubt,
you can use the “chkfsys” program to repair
corruption the file system. One thing to look
out for is that the last data written may not
be dumped to disk, but the file system may
not be aware of this. In this case you might
read a file and see bad data, the previous
information that was in the disk block.
Mitchell Schoenbrun --------- maschoen@pobox.com
Ivar Nilsson <ivar.nilsson@traffic.combitech.se> wrote in message
news:39a0d0ba.4610759@news.combitech.se…
Hi!
Is there anybody out there who knows how QNX’s (4.24) file system behaves
when the system are shot down in a non controlled way, i.e loss of power?
It doesn’t work anymore.
(Sorry. I couldn’t resist. Mitchell’s answer is actually quite good.)
On Tue, 22 Aug 2000 “Bill at Sierra Design” wrote:
Is there anybody out there who knows how QNX’s (4.24) file system behaves
when the system are shot down in a non controlled way, i.e loss of power?
It doesn’t work anymore.
That was noticed, they wonder way 
No the problem acctully is that the darn machine wont boot when they get
power again. But I suppose that the filesystem is not to blaim.
Maybe something that is able to corrupt the BIOS (maybe a loveletter-virus
for QNX!!)
(Sorry. I couldn’t resist. Mitchell’s answer is actually quite good.)
Yup!
/Ivar
Ivar Nilsson <ivar.nilsson@traffic.combitech.se> wrote in message
news:39a49128.184970173@news.combitech.se…
On Tue, 22 Aug 2000 “Bill at Sierra Design” wrote:
Is there anybody out there who knows how QNX’s (4.24) file system
behaves
when the system are shot down in a non controlled way, i.e loss of
power?
It doesn’t work anymore.That was noticed, they wonder way >
No the problem acctully is that the darn machine wont boot when they get
power again. But I suppose that the filesystem is not to blaim.
OK. At the risk of being slightly more helpful, are you talking about a
momentary loss of power, i.e.1 or 2 seconds or less?
I have seen many hardware devices that need all of their little capacitors
to power down (or whatever is happening) before they will power up again
correctly.
Does shutting the power down for at least 10 seconds solve the problem?
If not, what must you do to recover?