RE: AoE INT13h progress

> James Harper wrote:
> >
> > Yep. Also, it is possible to figure out the geometry by reading the
> > partition table on an already partitioned disk, which I believe the
> > linux kernel does. With a combination of:
> >
> > . AoE's geometry info
> > . HEADS=255, SECTORS=63, CYL=(Total Blocks) / 63 / 255
> > . Partition table derived
> >
> 
> Actually, you don't want to do the latter for something like AoE.
Since
> it's ATA, it really should behave as ATA BIOSes do.

With the latter, it allows the BIOS to assume the geometry that the disk
was partitioned with. Not doing so can get you into all sorts of
trouble. But maybe have it as optional rather than default behaviour...

> >>You only need
> >>to turn AoE booting on and off if your AoE code is resident, but I
> >> would suggest not doing that, and instead let the AoE-capable code
be a
> >>secondary download, so that it can be updated centrally.
> >
> > The beauty of AoE is that it requires no tcp/ip stack at all, just
the
> > ability to send and receive Ethernet frames. No DHCP server or
anything.
> > My idea is that you can put a new ((E)EP)ROM/Flash on a network card
and
> > suddenly it becomes an AoE initiator. If you are relying on a server
to
> > tftp code from then you might as well just use an initramfs.
> >
> 
> ... assuming you're running Linux as your target operating system (in
> which case, yes, you really might as well use initramfs.)
> 
> > The one thing in the settings that I forgot to mention is some way
to
> > nominate which shelf & slot to boot from. This would require 3 bytes
of
> > nv (2 for shelf, one for slot) storage. Most network cards have a
serial
> > eeprom that stores the MAC address and some other info. Maybe there
is
> > room in there, although (I think) Etherboot doesn't have a standard
> > interface for accessing it. That leaves some spare CMOS space in the
> > BIOS, which almost certainly isn't consistent between PC's. Maybe we
can
> > use the bytes from the existing harddisk specification...
> 
> Even if there is, for many cards there simply is no unused space,
> period.  Thus, you can't really rely on that space being available.

D'oh!
> 
> Hence I think you really want a central discovery server, and might as
> well use it to download the AoE stack.

AoE is designed as a SAN protocol, and it is conceivable that no servers
actually have local disks, and that a DHCP/TFTP server might not be
available. Also, it would be another point of failure unless the SAN
could provide this information... hmmm... definitely warrants more
discussion.

James


-------------------------------------------------------
This SF.net email is sponsored by: Splunk Inc. Do you grep through log files
for problems?  Stop!  Download the new AJAX search engine that makes
searching your log files as easy as surfing the  web.  DOWNLOAD SPLUNK!
http://ads.osdn.com/?ad_idv37&alloc_id865&op=click