From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jack Wang Subject: bcache strange behaviour in write back mode Date: Mon, 22 Apr 2013 21:15:14 +0200 Message-ID: <51758C42.4040708@profitbricks.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Sender: linux-bcache-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: linux-bcache-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, koverstreet-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org Cc: dongsu.park-EIkl63zCoXaH+58JC4qpiA@public.gmane.org List-Id: linux-bcache@vger.kernel.org Hi all, We've seen strange behaviour in bcache mode in current bcache-testing branch with Possible allocator fix: Once I start writing data with "dd if=/dev/zero of=/dev/bcache0 bs=4k count=10000 oflag=sync", all SSDs in the Pool go close to 100% util and I see about 3600 writes/second in iostat for each disk in the pool, BUT no data written in means of throughput. Then after some seconds (the flush interval of bcache) I see the flush of the writeback and also data written to the pool SSDs which looks pretty much like reordering and merging happened for that data. bcache-3.2 does not have such problem. only bcache(master) and bcache-testing have such problem. What's the possible reason? Regards, Jack