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What happens when the physical volume of an OST is irrecoverably lost? What data is lost? Only the data stored on this OST, or everything? And, if the first is true, how can one control what data is stored on which OST? Assuming that clients see a single combined filesystem.

Pim Schellart
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You lose any files which were striped onto that OST.

Lustre lets you control striping independently for each directory or file, using the lfs setstripe and lfs getstripe commands to control and view that configuration. You can configure the stripe size, stripe count, which OST to start striping on, etc.

By default Lustre has a default stripe count of 1 for each file (so that only one OST will contain that file), and subsequent files are assigned to different stripes in a round-robin fashion. However, most sites I've worked with set a default stripe of multiple OSTs for better performance. The Lustre manual has a lot more information on configuring striping.

Ideally each of your OSTs should be a RAID volume, not a single disk, so that you can guard against single-disk failures. AFAIK, Lustre doesn't provide any redundancy on its own.

ajdecon
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