From: Pavel Goran <via-bcache@pvgoran.name>
To: Nix <nix@esperi.org.uk>
Cc: Coly Li <colyli@suse.de>,
linux-bcache@vger.kernel.org, linux-block@vger.kernel.org
Subject: Re[2]: [PATCH v3 00/13] bcache: device failure handling improvement
Date: Thu, 25 Jan 2018 06:35:16 +0300 [thread overview]
Message-ID: <1664591662.20180125063516@pvgoran.name> (raw)
In-Reply-To: <87po5ykiaw.fsf@esperi.org.uk>
Hello Nix,
Thursday, January 25, 2018, 1:23:19 AM, you wrote:
> On 14 Jan 2018, Coly Li said:
>> Hi maintainers and folks,
>>
>> This patch set tries to improve bcache device failure handling, includes
>> cache device and backing device failures.
>>
>> The basic idea to handle failed cache device is,
>> - Unregister cache set
>> - Detach all backing devices which are attached to this cache set
>> - Stop all the detached bcache devices
>> - Stop all flash only volume on the cache set
>> The above process is named 'cache set retire' by me. The result of cache
>> set retire is, cache set and bcache devices are all removed, following
>> I/O requests will get failed immediately to notift upper layer or user
>> space coce that the cache device is failed or disconnected.
> This feels wrong to me. If a cache device is writethrough, the cache is
> a pure optimization: having such a device fail should not lead to I/O
> failures of any sort, but should only flip the cache device to 'none' so
> that writes to the backing store simply don't get cached any more.
> Anything else leads to a reliability reduction, since in the end cache
> devices *will* fail.
It's one of those choices: "if something can't work as intended, should it be
allowed to work at all?" I believe different use cases will have different
answers to this question. So ideally this should be configurable by some kind
of option stored in superblock, much like the "Errors behavior" option of ext*
filesystems.
Of course, this only applies to "writethrough" and "writearound" modes with
zero dirty data; "writeback" bcache devices (or devices switched from
writeback and still having some dirty data) should probably be disabled if the
cache device fails.
Pavel Goran
next prev parent reply other threads:[~2018-01-25 3:35 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-14 14:42 [PATCH v3 00/13] bcache: device failure handling improvement Coly Li
2018-01-14 14:42 ` [PATCH v3 01/13] bcache: set writeback_rate_update_seconds in range [1, 60] seconds Coly Li
2018-01-16 9:03 ` Hannes Reinecke
2018-01-14 14:42 ` [PATCH v3 02/13] bcache: properly set task state in bch_writeback_thread() Coly Li
2018-01-16 9:02 ` Hannes Reinecke
2018-01-14 14:42 ` [PATCH v3 03/13] bcache: set task properly in allocator_wait() Coly Li
2018-01-16 9:05 ` Hannes Reinecke
2018-01-16 9:29 ` Coly Li
2018-01-14 14:42 ` [PATCH v3 04/13] bcache: fix cached_dev->count usage for bch_cache_set_error() Coly Li
2018-01-14 14:42 ` [PATCH v3 05/13] bcache: quit dc->writeback_thread when BCACHE_DEV_DETACHING is set Coly Li
2018-01-16 9:11 ` Hannes Reinecke
2018-01-26 6:21 ` Coly Li
2018-01-14 14:42 ` [PATCH v3 06/13] bcache: stop dc->writeback_rate_update properly Coly Li
2018-01-14 14:42 ` [PATCH v3 07/13] bcache: set error_limit correctly Coly Li
2018-01-14 14:42 ` [PATCH v3 08/13] bcache: add CACHE_SET_IO_DISABLE to struct cache_set flags Coly Li
2018-01-14 14:42 ` [PATCH v3 09/13] bcache: stop all attached bcache devices for a retired cache set Coly Li
2018-01-14 14:42 ` [PATCH v3 10/13] bcache: fix inaccurate io state for detached bcache devices Coly Li
2018-01-16 9:27 ` Hannes Reinecke
2018-01-14 14:42 ` [PATCH v3 11/13] bcache: add backing_request_endio() for bi_end_io of attached backing device I/O Coly Li
2018-01-16 9:28 ` Hannes Reinecke
2018-01-14 14:42 ` [PATCH v3 12/13] bcache: add io_disable to struct cached_dev Coly Li
2018-01-16 9:32 ` Hannes Reinecke
2018-01-14 14:42 ` [PATCH v3 13/13] bcache: stop bcache device when backing device is offline Coly Li
2018-01-16 9:33 ` Hannes Reinecke
2018-01-24 22:23 ` [PATCH v3 00/13] bcache: device failure handling improvement Nix
2018-01-25 3:35 ` Pavel Goran [this message]
2018-01-25 18:57 ` Nix
2018-01-26 4:15 ` Re[2]: " Pavel Goran
2018-01-26 4:56 ` Coly Li
2018-01-26 5:51 ` Michael Lyle
2018-01-26 6:23 ` Coly Li
2018-02-16 12:11 ` Nix
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