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List:       linux-lvm
Subject:    Re: [linux-lvm] bcache now to become io-manager?
From:       "John Stoffel" <john () stoffel ! org>
Date:       2019-10-31 19:29:07
Message-ID: 23995.13827.23398.434894 () quad ! stoffel ! home
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>>>>> "Joe" == Joe Thornber <thornber@redhat.com> writes:

Joe> On Tue, Oct 29, 2019 at 08:25:23PM -0400, John Stoffel wrote:
>> >>>>> "Joe" == Joe Thornber <thornber@redhat.com> writes:
>> 
>> [ I saw this and couldn't resist asking for more details ...]
>> 
Joe> Also there are big changes to bcache coming, that remove file
Joe> descriptors from the interface completely.  See the branch
Joe> 2019-09-05-add-io-manager for more info (bcache has been renamed
Joe> io_manager).
>> 
>> Can you post the full URL for this, and maybe give us a teaser on what
>> to expect?  I run lvache on my home system and I'd love to know how to
>> A) improve reporting of how well it works, and B) whether I'm using it
>> right, and of course C) if bcache would be a better replacement.
>> 
>> I'm using Linux v5.0.21 (self compiled) on Debian 9.11 with lvcache
>> setup.  It's a pair of mirrored 250gb SSDs in front of 4tb of mirrored
>> disk.
>> 
>> So anything where I can use my SSDs to cache my data accesses is
>> certainly interesting.

Joe> Sorry, I think we're getting confused with similarly named
Joe> things.  There is a component in LVM source called 'block cache'
Joe> that we use to scan devices in parallel (under the hood it uses
Joe> aio).  That component is being renamed.  It's nothing to do with
Joe> the disk caching technology called 'bcache'.

Ah... that's a good reason for this rename then. 

Joe> However, Dave Teigland has been adding support to LVM for a new
Joe> caching target that emphasises caching writes.  So keep an eye
Joe> out for that.

Will do. It's never really been clear if lvcache has really helped or
not, the testing was in-conclusive.

John

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