[Beowulf] instances where a failed storage block is not all zero?

Greg Lindahl lindahl at pbm.com
Wed Jul 7 19:04:40 EDT 2010


On Wed, Jul 07, 2010 at 03:34:01PM -0700, David Mathog wrote:

> With "modern" hardware are there currently any notable instances where a
> failed read of a hardware storage area block results in that missing
> data being filled in with something other than null bytes?

Yes. You might get the wrong block due to a misdirected write or read,
or you might get an old block because the previous write experienced
"write tearing".

If the OS knows it was unable to read a block and replaced it with
zeros, it will throw an error. In Linux, the behavior depends on what
you chose: panic on error, mount r/o, or continue. If the nulls are
part of the filesystem metadata, all hell can break loose.

The errors in the first paragraph won't be detected at all. They're
rare, but...

-- greg


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