Re: MD/DM and barriers (was Re: [patch] ext2/3: document conditionswhen reliable operation is possible)

From: Michael Tokarev
Date: Wed Sep 02 2009 - 12:17:49 EST

Pavel Machek wrote:
On Thu 2009-08-27 12:54:05, Jeff Garzik wrote:
Only md/raid1 supports barriers at present, it seems. None of the other MD drivers support barriers.

Not even md/raid0? Ouch :-(.

Only for raid1 there's no requiriment for inter-drive ordering. Hence
only raid1 supports barriers (and gained that support very recently,
in 1 or 2 kernel releases). For the rest, including raid0 and linear,
inter-drive ordering is necessary to implement barriers. Or md should
have its own queue (flushing) mechanisms.

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