[Lustre-devel] Checksum Algorithm

Paul Nowoczynski pauln at psc.edu
Tue Nov 6 11:57:50 PST 2007

How does the crc mechanism work?  I assume that the crc is done at the 
client, does the server verify the crc?   Also are the crc's stored on disk?

Brian Behlendorf wrote:
> Roger,
>   We've been running with checksums enabled in our release for some time now
> and have seen the exact same impact on performance.  In our case single node
> performance is impacted but aggregate FS performance remains good when enough
> clients are involved.  We are tracking the performance issue under bug 13805
> and would love any input/insight you might have on the issue.
>   Bug13805 <https://bugzilla.lustre.org/show_bug.cgi?id=13805>
>   My view on the issue is that it is madness to run with checksums disabled
> and we need to investigate more efficient checksum algorithms.  The current
> crc32 algorithm may be too heavy weight but the simple XOR algorithm you
> propose I fear is not strong enough.  I've seen to many cases now of various
> network components corrupting data in all sorts of interesting ways.
> Happily we have a lot of other choices for algorithms to investigate.
>   If you have the time I'd encourage you to investigate an assortment of
> algorithms and see which work best.  Making this a runtime option via 
> proc I think is also an excellent idea.
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