[Beowulf] Re: RAID for home beowulf

Mark Hahn hahn at mcmaster.ca
Wed Oct 14 01:41:13 EDT 2009


> 3) Be aware that the kernel you are using will make a big
> difference and that the semantics for ext3 have changed
> a while ago so that it no longer uses data=ordered but
> instead uses data=writeback by default (you can override

AFAIKT, it's just an option for the default mount config now
that wasn't offered before.  major distros (I only checked fedora)
still do data=ordered, and the latest kernel snapshot still has 
data=ordered as the default.

the kernel config help text points to this:
http://ext4.wiki.kernel.org/index.php/Ext3_Data%3DOrdered_vs_Data%3DWriteback_mode
which makes a useful point about app-level consistency still requiring 
fsyncs (which operates above any fs-level consistency guarantees.)

also, I find swapfiles more convenient than partitions.  some installers
always force a swap partition to the tail of the disk, which is pessimal.

regards, mark hahn.
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