Re: [Libguestfs] [PATCH] New API: mdadm-stop for stopping MD devices.

On 23/11/11 17:11, Matthew Booth wrote: > On 23/11/11 16:22, Richard W.M. Jones wrote: >> On Wed, Nov 23, 2011 at 03:02:19PM +0000, Matthew Booth wrote: >>> On 23/11/11 14:43, Wanlong Gao wrote: >>>> This API is used to stop a md device. >>>> When we want to move a device to another md array, we should >>>> stop the md device which contained this device first. >>> >>> I'm not convinced we should extend the md api in libguestfs to >>> active manipulation. I wasn't convinced that mdadm-create was >>> worthwhile either, but it made a test case ever so slightly tidier. >>> To me, MD devices are the domain of physical machines. We need to be >>> able to *read* them (for P2V apart from anything else), but I think >>> manipulation is opening an unnecessary can of worms. >> >> But is there any penalty to carrying this? > > I can think of 2: > > 1. Maintenance: I know you think this is free, but some day mdadm --stop > might change behaviour, and then the api will break. > > 2. A false sense of expectation: Having an incomplete md api can only > lead to frustration. Implementing a complete md api would require a > large amount of effort for something which we don't have a convincing > use case for (i.e. nobody's ever going to use it anyway). There's another good one, actually: Testing. mdadm-create has already created a testing problem, because test-mdadm.sh fails mysteriously on my machine, but didn't before and doesn't for you or Wanlong. Especially

for something like MD, which has a complex subsystem underlying it which we don't fully understand in our team, adding and adequately testing a new API is an expensive operation.

Matt