QNX4 Fsys and the -a option

We are currently developing a PC system using QNX4 and SanDisk CF instead of
a hard drive. Now the system has
a battery backup for 2 minutes to make sure we close down the filesystem on
a power loss. Our main concern is the
slower access speed of the CF compared to the hard drive. I’m looking at
using the Fsys -a option, actually the
command line would be something like ‘Fsys -a -d4 -c 8M’. I’ve read that
the ‘-a’ option only affects ‘system files’.
What are these, are they only bitmaps, inodes, directory entries, etc. Or
does this include any file being written to
the CF? Thanks for any help.


Ivan Bannon
Software Development Manager
RJG Inc.
ivan.bannon@rjginc.com

“Ivan Bannon” <ivan.bannon@rjginc.com> wrote in message
news:bhrchb$bmu$1@inn.qnx.com

We are currently developing a PC system using QNX4 and SanDisk CF instead
of
a hard drive. Now the system has
a battery backup for 2 minutes to make sure we close down the filesystem
on
a power loss. Our main concern is the
slower access speed of the CF compared to the hard drive. I’m looking at
using the Fsys -a option, actually the
command line would be something like ‘Fsys -a -d4 -c 8M’. I’ve read that
the ‘-a’ option only affects ‘system files’.
What are these, are they only bitmaps, inodes, directory entries, etc. Or
does this include any file being written to
the CF?

To my knowledge it affects everything. Note that it won’t make writing to
disk any faster. You application may see it as faster, but you could still
get a worst case scenario if the case fills up. As a matter of fact this
can cause some strange behavior. Let’s say an application writes 4 megs of
data. All the data goes in the cache and the application write calls take
very little time. But then 4 seconds latter (-d4) Fsys flushes the data on
the CF, the flushing will perform at the priority of Fsys.ide and not at the
priority of the client. Hence all processes of lower priority may by
“unexpectedly” be denied CPU time for a very long time (4Meg of data can
easely take 10sec).

Thanks for any help.


Ivan Bannon
Software Development Manager
RJG Inc.
ivan.bannon@rjginc.com

Thanks Mario, that appears to be what I’m seeing. I’d like to continue
using hard drives but the
environment is too hot (+70C), and has too much vibration. I’m going to
play around with the
delay and cache options to try to find an optimum setting, or get rid of
‘-a’ all together.

Thanks again


Ivan Bannon
Software Development Manager
RJG Inc.
ivan.bannon@rjginc.com
“Mario Charest” postmaster@127.0.0.1 wrote in message
news:bhre69$clc$1@inn.qnx.com

“Ivan Bannon” <> ivan.bannon@rjginc.com> > wrote in message
news:bhrchb$bmu$> 1@inn.qnx.com> …
We are currently developing a PC system using QNX4 and SanDisk CF
instead
of
a hard drive. Now the system has
a battery backup for 2 minutes to make sure we close down the filesystem
on
a power loss. Our main concern is the
slower access speed of the CF compared to the hard drive. I’m looking
at
using the Fsys -a option, actually the
command line would be something like ‘Fsys -a -d4 -c 8M’. I’ve read
that
the ‘-a’ option only affects ‘system files’.
What are these, are they only bitmaps, inodes, directory entries, etc.
Or
does this include any file being written to
the CF?

To my knowledge it affects everything. Note that it won’t make writing to
disk any faster. You application may see it as faster, but you could
still
get a worst case scenario if the case fills up. As a matter of fact this
can cause some strange behavior. Let’s say an application writes 4 megs
of
data. All the data goes in the cache and the application write calls take
very little time. But then 4 seconds latter (-d4) Fsys flushes the data
on
the CF, the flushing will perform at the priority of Fsys.ide and not at
the
priority of the client. Hence all processes of lower priority may by
“unexpectedly” be denied CPU time for a very long time (4Meg of data can
easely take 10sec).

Thanks for any help.


Ivan Bannon
Software Development Manager
RJG Inc.
ivan.bannon@rjginc.com
\

Ivan Bannon <ivan.bannon@rjginc.com> wrote:

environment is too hot (+70C), and has too much vibration. I’m going to
play around with the delay and cache options to try to find an optimum
setting, or get rid of ‘-a’ all together.

‘-a’ will gain you something by allowing system writes to be shared
(combine multiple bitmap/inode operations into a single physical access),
and should probably be used given you have UPS. Possibly reduce the ‘-d’
down to 1 or 2 seconds to help reduce dirty cache overflow. Consider using
‘-A’ for flash to not do writes (inode atime) when simply reading.

Ivan Bannon <ivan.bannon@rjginc.com> wrote:
IB > Thanks Mario, that appears to be what I’m seeing. I’d like to continue
IB > using hard drives but the
IB > environment is too hot (+70C), and has too much vibration. I’m going to
IB > play around with the
IB > delay and cache options to try to find an optimum setting, or get rid of
IB > ‘-a’ all together.

IB > Thanks again

Are you appending large amounts of serial data or are you updating
blocks of a file that already exists? That would affect how I changed
the system.

You may try just reducing the cache size (-C) if your appending a lot
of new data, or reducing the delay (-d) if your doing random updates.
This would keep your data in cache for subsequent reads.

There are several issues of diminishing returns for very large caches.
On slower CPUs it may take longer to do cache lookups then it would to
just read the damn stuff.


Bill Caroselli – Q-TPS Consulting
1-(626) 824-7983
qtps@earthlink.net

Ivan Bannon wrote:

We are currently developing a PC system using QNX4 and SanDisk CF instead of
a hard drive. Now the system has
a battery backup for 2 minutes to make sure we close down the filesystem on
a power loss. Our main concern is the
slower access speed of the CF compared to the hard drive. I’m looking at
using the Fsys -a option, actually the
command line would be something like ‘Fsys -a -d4 -c 8M’. I’ve read that
the ‘-a’ option only affects ‘system files’.
What are these, are they only bitmaps, inodes, directory entries, etc. Or
does this include any file being written to
the CF? Thanks for any help.


Ivan Bannon
Software Development Manager
RJG Inc.
ivan.bannon@rjginc.com

Try to use MSystem products: Disk OnChip family it has a native drivers.


Mariusz Hawryluk
PBiWH “Next” s.c.
Warszawa