From: NeilBrown <neilb@suse.com>
To: linux-raid@vger.kernel.org
Cc: shli@fb.com, kernel-team@fb.com, dan.j.williams@intel.com,
hch@infradead.org, liuzhengyuang521@gmail.com,
liuzhengyuan@kylinos.cn, Song Liu <songliubraving@fb.com>
Subject: Re: [PATCH v5 7/8] md/r5cache: r5c recovery
Date: Wed, 19 Oct 2016 13:32:48 +1100 [thread overview]
Message-ID: <87inspxe3z.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <20161013054944.1038806-8-songliubraving@fb.com>
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On Thu, Oct 13 2016, Song Liu wrote:
> This is the recovery part of raid5-cache.
>
> With cache feature, there are 2 different scenarios of recovery:
> 1. Data-Parity stripe: a stripe with complete parity in journal.
> 2. Data-Only stripe: a stripe with only data in journal (or partial
> parity).
>
> The code differentiate Data-Parity stripe from Data-Only stripe with
> flag (STRIPE_R5C_WRITTEN).
>
> For Data-Parity stripes, we use the same procedure as raid5 journal,
> where all the data and parity are replayed to the RAID devices.
>
> For Data-Only strips, we need to finish complete calculate parity and
> finish the full reconstruct write or RMW write. For simplicity, in
> the recovery, we load the stripe to stripe cache. Once the array is
> started, the stripe cache state machine will handle these stripes
> through normal write path.
>
> r5c_recovery_flush_log contains the main procedure of recovery. The
> recovery code first scans through the journal and loads data to
> stripe cache. The code keeps tracks of all these stripes in a list
> (use sh->lru and ctx->cached_list), stripes in the list are
> organized in the order of its first appearance on the journal.
> During the scan, the recovery code assesses each stripe as
> Data-Parity or Data-Only.
>
> During scan, the array may run out of stripe cache. In these cases,
> the recovery code will also call raid5_set_cache_size to increase
> stripe cache size.
What if this fails. Maybe the array was created on a machine with lots
or memory, but that machine died and you are trying to recovery you data
on a much less capable machine.
I don't think there is an easy answer, but at least you need to fail
gracefully.
I'll try to look at the rest tomorrow.
NeilBrown
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next prev parent reply other threads:[~2016-10-19 2:32 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-13 5:49 [PATCH v5 0/8] raid5-cache: enabling cache features Song Liu
2016-10-13 5:49 ` [PATCH v5 1/8] md/r5cache: Check array size in r5l_init_log Song Liu
2016-10-13 5:49 ` [PATCH v5 2/8] md/r5cache: move some code to raid5.h Song Liu
2016-10-13 5:49 ` [PATCH v5 3/8] md/r5cache: State machine for raid5-cache write back mode Song Liu
2016-10-14 6:13 ` NeilBrown
2016-10-14 7:03 ` Song Liu
2016-10-13 5:49 ` [PATCH v5 4/8] md/r5cache: write part of r5cache Song Liu
2016-10-14 6:53 ` NeilBrown
2016-10-14 7:33 ` Song Liu
2016-10-19 0:53 ` NeilBrown
2016-10-21 20:42 ` Song Liu
2016-10-13 5:49 ` [PATCH v5 5/8] md/r5cache: reclaim support Song Liu
2016-10-19 2:03 ` NeilBrown
2016-10-21 21:04 ` Song Liu
2016-10-13 5:49 ` [PATCH v5 6/8] md/r5cache: sysfs entry r5c_state Song Liu
2016-10-19 2:19 ` NeilBrown
2016-10-21 21:20 ` Song Liu
2016-10-13 5:49 ` [PATCH v5 7/8] md/r5cache: r5c recovery Song Liu
2016-10-19 2:32 ` NeilBrown [this message]
2016-10-20 3:03 ` NeilBrown
2016-10-21 21:12 ` Song Liu
2016-10-26 1:18 ` NeilBrown
2016-10-13 5:49 ` [PATCH v5 8/8] md/r5cache: handle SYNC and FUA Song Liu
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