Re: [PATCH, RFC] xfs: batched discard support

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On 08/19/2009 09:39 PM, Mark Lord wrote:
[resending, after fixing the Cc: list; somebody trimmed it earlier]

Jamie Lokier wrote:
..
I don't remember - does TRIM guarantee the blocks read zeros afterwards?
..

No, it doesn't.

A drive can optionally support "deterministic TRIM", whereby it will return consistent data for any given trimmed sector afterwards, but that doesn't mean zeros.

-ml

Note that returning consistent data is critical for devices that are used in a RAID group since you will need each RAID block that is used to compute the parity to continue to return the same data until you overwrite it with new data :-)

If we have a device that does not support this (or is misconfigured not to do this), we should not use those devices in an MD group & do discard against it...

ric

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