From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jonathan Tripathy Subject: Bcache in Xen Environment Date: Wed, 01 Aug 2012 10:20:15 +0100 Message-ID: <5fe181f7719e9d85f15e0906688388bd@abpni.co.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Sender: linux-bcache-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: linux-bcache-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-bcache@vger.kernel.org Hi Everyone, I wish to investigate using bcache in a Xen virtualisation environment. We wish to use bcache to add a SSD (single drive) cache to a RAID10 device (using metal spindles), and I have a few questions. 1) On the bcache website, it says this: "It won't return a write as completed until everything necessary to locate it is on stable storage, nor will writes ever be seen as partially completed (or worse, missing) in the event of power failure." Is this just true for write-through? Or write-back mode as well? If it is true for write-back mode, how does this work? I thought the point of write-back mode was to return write quickly due to the fast buffer storage. 2) When we delete a virtual machine, it is common for us to run dd to "zero" the LVM LV so that data is deleted. If we introduce bcache, can we still be sure that all data is gone? We need to make sure that no data leakage can occur between LVs. 3) SSD storage has a much more limited write span that metal spindles. If an SSD drive were to fail, will the RAID10 spindle array still continue to function? Will any data be lost? How does write-through and write-back handle these cases? Thanks for your time.