[sheepdog] [PATCH 0/8] add basic raid support

[MORITA Kazutaka]

At Mon, 11 Mar 2013 10:17:03 +0800,
Liu Yuan wrote:
> 
> On 03/11/2013 08:55 AM, MORITA Kazutaka wrote:
> > At Sun, 10 Mar 2013 22:19:21 +0800,
> > Liu Yuan wrote:
> >>
> >> From: Liu Yuan <tailai.ly at taobao.com>
> >>
> >> This patch set implements the basic RAID support that aims to manage multiple
> >> disks in one node. 
> >>
> >> The basic idea of this RAID is implement RAID-0 like mechanism that distributes
> >> sheep objects on the local disks without parity or replicating, which instead 
> >> relies on the sheepdog's replicated storage to recover the lost objects on the 
> >> faulty disk.
> >>
> >> The raid module use a private consistent hash ring per sheep for object
> >> distributing, which allow raid layer completely transparent to sheep node
> >> managent. This means that hot plug/unplug the disk (include faulty disks) to the
> >> local sheep won't cause object movement between the nodes.
> >>
> >> This series just implement basic object distribution control of raid module. The
> >> missing part is internal object recovery between local disks inside the node and
> >> collie command to hot plug/unplug the disk into the sheep daemon, which is meant
> >> to be written by the next series.
> > 
> > So can we set the redundancy level of the raid module in the next series?
> > 
> 
> No. I plan to recover lost objects from other sheep. Maybe What I wrote
> is kind of misleading. With copy=1, we maximize the disk space
> utilization and performance, resulting in simpler code too.

Okay, understood.

IMHO, if you have no plan to specify the redundant level, it is
misleading to name the feature raid (redundant arrays of independent
disks).  I'd suggest other names to , e.g., raid0, striping, md
(multidisk), ...

> I think meta-store can be placed at operating system partition, which is
> a SPOF too. And if this partition is broken, however many replica we
> have for sheep will not stop this sheep from being broken. My argument
> is that placing meta-store with OS partition is simple and achieve the
> same actual level of fault tolerant. (People can make RAID for this
> partition).

Agreed.

Thanks,

Kazutaka