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Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices



Alasdair G Kergon wrote:
On Fri, Feb 15, 2008 at 03:20:10PM +0100, Andi Kleen wrote:
On Fri, Feb 15, 2008 at 04:07:54PM +0300, Michael Tokarev wrote:
I wonder if it's worth the effort to try to implement this.

My personal view (which seems to be in the minority) is that it's a
waste of our development time *except* in the (rare?) cases similar to
the ones Andi is talking about.

Using working barriers is important for normal users when you really care about data loss and have normal drives in a box. We do power fail testing on boxes (with reiserfs and ext3) and can definitely see a lot of file system corruption eliminated over power failures when barriers are enabled properly.

It is not unreasonable for some machines to disable barriers to get a performance boost, but I would not do that when you are storing things you really need back.

Of course, you don't need barriers when you either disable the write cache on the drives or use a battery backed RAID array which gives you a write cache that will survive power outages...

ric


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