Scyld and fstab for Diskless slaves

Daniel Ridge newt at scyld.com
Fri Dec 15 13:15:27 EST 2000


On Fri, 15 Dec 2000, David Leunen wrote:

> But I have another prob: How to configure /etc/beowulf/fstab correctly
> for diskless nodes? I didn't see anything about diskless in the doc.

For reference, the details of the slave fstab file are in the Beowulf
install guide bundled with our distribution. To summarize:

Configuring ramdisks for Scyld Beowulf is straightforward.
Comment or remove the '/' and 'swap' entries from /etc/beowulf/fstab.
Create a line which looks like:

/dev/ram3	/	ext2	fs_size=65536	0 0

The magic bit is that we have added a mount option -- fs_size -- that
tells us how large to make the disk.

This relates to another question asked recently in this forum:
	Why does our default kernel command line specify a ramdisk_size
	of 128M?

This should be pretty safe on boxes that don't even have 128M -- but
you will get into trouble if you try to use the large ramdisks. If
you have troubles installing Scyld Beowulf -- this isn't the problem.

Also, while we set up a beefy ramdisk during boot -- this space is
reclaimed when the node finishes booting if you aren't doing a ramdisk
root.

This, in turn, relates to another freqeuntly asked question:
	Why do my nodes show up as unavailable?

The reason is usually that the default fstab (/etc/beowulf/fstab) does
not relate to the partitioning on your disks. Whatever the reason,
the details of the node boot do not appear on the console. This record
can be found in /var/log/beowulf/node.<nodenum> where <nodenum> is the
node number that you seek.

Our upcoming contains a lot of effort directed towards reducing the size
of ramdisk. This is to make the system work on smaller memory machines
and to make diskless operation more palatable on medium memory machines. I
have run our upcoming version on VMware instances with as little as 16M
with a beowulf ram footprint of about 2M.

Because we can now do this, I expect that the next version of our product
will ship with ramdisk root as the default.

Regards,
	Dan Ridge
	Scyld Computing Corporation




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