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

[Michael Tokarev]

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.

/mjt
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