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From: Eric Wheeler <bcache@lists.ewheeler.net>
To: Christoph Hellwig <hch@infradead.org>
Cc: Keith Busch <kbusch@kernel.org>, Coly Li <colyli@suse.de>,
	Adriano Silva <adriano_da_silva@yahoo.com.br>,
	Bcache Linux <linux-bcache@vger.kernel.org>,
	Matthias Ferdinand <bcache@mfedv.net>,
	linux-block@vger.kernel.org
Subject: Re: [RFC] Add sysctl option to drop disk flushes in bcache? (was: Bcache in writes direct with fsync)
Date: Wed, 25 May 2022 11:44:01 -0700 (PDT)	[thread overview]
Message-ID: <77e7dbf9-d5bd-424-1ef7-8a1bb49e9010@ewheeler.net> (raw)
In-Reply-To: <Yo28kDw8rZgFWpHu@infradead.org>

On Tue, 24 May 2022, Christoph Hellwig wrote:
> On Tue, May 24, 2022 at 02:34:23PM -0700, Eric Wheeler wrote:
> > Is this flag influced at all when /sys/block/sdX/queue/scheduler is set 
> > to "none", or does the write_cache flag operate independently of the 
> > selected scheduler?
> 
> This is up to the stacking driver.  dm and tend to pass through flushes
> where needed.
> 
> > This confirms what I have suspected all along: We have an LSI MegaRAID 
> > SAS-3516 where the write policy is "write back" in the LUN, but the cache 
> > is flagged in Linux as write-through:
> > 
> > 	]# cat /sys/block/sdb/queue/write_cache 
> > 	write through
> > 
> > I guess this is the correct place to adjust that behavior!
> 
> MegaRAID has had all kinds of unsafe policies in the past unfortunately.
> I'm not even sure all of them could pass through flushes properly if we
> asked them to :(

Thanks for the feedback, great info!

In your experience, which SAS/SATA RAID controllers are best behaved in 
terms of policies and reporting things like io_opt and 
writeback/writethrough to the kernel?

  reply	other threads:[~2022-05-25 18:44 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <958894243.922478.1652201375900.ref@mail.yahoo.com>
2022-05-10 16:49 ` Bcache in writes direct with fsync. Are IOPS limited? Adriano Silva
2022-05-11  6:20   ` Matthias Ferdinand
2022-05-11 12:58     ` Adriano Silva
2022-05-11 21:21       ` Matthias Ferdinand
2022-05-18  1:22   ` Eric Wheeler
2022-05-23 14:07     ` Coly Li
2022-05-26 19:15       ` Eric Wheeler
2022-05-27 17:28         ` colyli
2022-05-28  0:58           ` Eric Wheeler
2022-05-23 18:36     ` [RFC] Add sysctl option to drop disk flushes in bcache? (was: Bcache in writes direct with fsync) Eric Wheeler
2022-05-24  5:34       ` Christoph Hellwig
2022-05-24 20:14         ` Eric Wheeler
2022-05-24 20:34           ` Keith Busch
2022-05-24 21:34             ` Eric Wheeler
2022-05-25  5:20               ` Christoph Hellwig
2022-05-25 18:44                 ` Eric Wheeler [this message]
2022-05-26  9:06                   ` Christoph Hellwig
2022-05-28  1:52                 ` Eric Wheeler
2022-05-28  3:57                   ` Keith Busch
2022-05-28  4:59                   ` Christoph Hellwig
2022-05-28 12:57                     ` Adriano Silva
2022-05-29  3:18                       ` Keith Busch
2022-05-31 19:42                         ` Eric Wheeler
2022-05-31 20:22                           ` Keith Busch
2022-05-31 23:04                             ` Eric Wheeler
2022-06-01  0:36                               ` Keith Busch
2022-06-01 18:48                                 ` Eric Wheeler
     [not found]                         ` <2064546094.2440522.1653825057164@mail.yahoo.com>
     [not found]                           ` <YpTKfHHWz27Qugi+@kbusch-mbp.dhcp.thefacebook.com>
2022-06-01 19:27                             ` Adriano Silva
2022-06-01 21:11                               ` Eric Wheeler
2022-06-02  5:26                                 ` Christoph Hellwig
2022-05-25  5:17           ` Christoph Hellwig
     [not found]     ` <681726005.1812841.1653564986700@mail.yahoo.com>
2022-05-26 20:20       ` Bcache in writes direct with fsync. Are IOPS limited? Adriano Silva
2022-05-26 20:28       ` Eric Wheeler
2022-05-27  4:07         ` Adriano Silva
2022-05-28  1:27           ` Eric Wheeler
2022-05-28  7:22             ` Matthias Ferdinand
2022-05-28 12:09               ` Adriano Silva

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