From: NeilBrown <neilb@suse.com>
To: Artur Paszkiewicz <artur.paszkiewicz@intel.com>, shli@kernel.org
Cc: linux-raid@vger.kernel.org
Subject: Re: [PATCH v2 00/12] Partial Parity Log for MD RAID 5
Date: Wed, 07 Dec 2016 11:32:09 +1100 [thread overview]
Message-ID: <87fum04m0m.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <20161205153113.7268-1-artur.paszkiewicz@intel.com>
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On Tue, Dec 06 2016, Artur Paszkiewicz wrote:
> This series of patches implements the Partial Parity Log for RAID5 arrays. The
> purpose of this feature is closing the RAID Write Hole. It is a solution
> alternative to the existing raid5-cache, but the implementation is based on it
> and reuses some of the code by introducing support for interchangeable
> policies. This allows decoupling policy from mechanism and not adding more
> boilerplate code in raid5.c.
>
> The issue addressed by PPL is, that on a dirty shutdown, parity for a
> particular stripe may be inconsistent with data on other member disks. In
> degraded state, there is no way to recalculate parity, because one of the disks
> is missing. PPL addresses this issue and allows recalculating the parity. It
> stores only enough data needed for recovering from RWH and is not a true
> journal, like the raid5-cache implementation. It does not protect from losing
> in-flight data.
>
> PPL is a distributed log - data is stored on all RAID member drives in the
> metadata area. It does not need a dedicated journaling drive. Performance is
> reduced by up to 30%-40% but it scales with the number of drives in the array
> and the journaling drive does not become a bottleneck.
I would expect to see as description of what a PPL actually is and how
it works here... but there is none.
The change-log for patch 06 has a tiny bit more information which is
just enough to be able to start trying to understand the code, but it
isn't much.
And none of this description gets into the code, or into the
Documentation/. This makes it hard to review and hard to maintain.
Remember: if you want people to review you code, it is in your interest
to make it easy. That means give lots of details.
NeilBrown
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next prev parent reply other threads:[~2016-12-07 0:32 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-05 15:31 [PATCH v2 00/12] Partial Parity Log for MD RAID 5 Artur Paszkiewicz
2016-12-05 15:31 ` [PATCH v2 01/12] raid5-cache: move declarations to separate header Artur Paszkiewicz
2016-12-05 15:31 ` [PATCH v2 02/12] raid5-cache: add policy logic Artur Paszkiewicz
2016-12-05 15:31 ` [PATCH v2 03/12] raid5-cache: add a new policy Artur Paszkiewicz
2016-12-07 0:46 ` NeilBrown
2016-12-07 14:36 ` Artur Paszkiewicz
2016-12-07 23:24 ` NeilBrown
2016-12-08 10:28 ` Artur Paszkiewicz
2016-12-08 21:22 ` NeilBrown
2016-12-05 15:31 ` [PATCH v2 04/12] md: superblock changes for PPL Artur Paszkiewicz
2016-12-05 15:31 ` [PATCH v2 05/12] raid5-ppl: Partial Parity Log implementation Artur Paszkiewicz
2016-12-06 1:06 ` kbuild test robot
2016-12-07 1:17 ` NeilBrown
2016-12-07 14:37 ` Artur Paszkiewicz
2016-12-05 15:31 ` [PATCH v2 06/12] raid5-ppl: calculate partial parity Artur Paszkiewicz
2016-12-05 15:31 ` [PATCH v2 07/12] md: mddev_find_container helper function Artur Paszkiewicz
2016-12-07 1:23 ` NeilBrown
2016-12-05 15:31 ` [PATCH v2 08/12] md: expose rdev->sb_start as sysfs attribute Artur Paszkiewicz
2016-12-07 1:25 ` NeilBrown
2016-12-05 15:31 ` [PATCH v2 09/12] raid5-ppl: read PPL signature from IMSM metadata Artur Paszkiewicz
2016-12-07 1:25 ` NeilBrown
2016-12-07 14:38 ` Artur Paszkiewicz
2016-12-07 23:27 ` NeilBrown
2016-12-08 10:36 ` Artur Paszkiewicz
2016-12-05 15:31 ` [PATCH v2 10/12] raid5-ppl: recovery from dirty shutdown using PPL Artur Paszkiewicz
2016-12-05 15:31 ` [PATCH v2 11/12] raid5-ppl: support disk add/remove with distributed PPL Artur Paszkiewicz
2016-12-07 1:29 ` NeilBrown
2016-12-05 15:31 ` [PATCH v2 12/12] raid5-ppl: runtime PPL enabling or disabling Artur Paszkiewicz
2016-12-07 0:32 ` NeilBrown [this message]
2016-12-07 14:36 ` [PATCH v2 00/12] Partial Parity Log for MD RAID 5 Artur Paszkiewicz
2016-12-07 17:09 ` Shaohua Li
2016-12-13 15:25 ` Jes Sorensen
2016-12-14 19:47 ` Shaohua Li
2016-12-15 11:44 ` Artur Paszkiewicz
2016-12-16 23:24 ` Shaohua Li
2017-01-03 15:42 ` Jes Sorensen
2017-01-04 8:01 ` Artur Paszkiewicz
2017-01-04 13:29 ` Jes Sorensen
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