From: Vojtech Pavlik <vojtech@suse.com>
To: Pradeep Jindal <praddyjindal@gmail.com>
Cc: linux-bcache@vger.kernel.org
Subject: Re: 84% -> 60% cache hit ratio for same workflow, different conf
Date: Mon, 28 Mar 2016 22:19:07 +0200 [thread overview]
Message-ID: <20160328201907.GA20296@suse.cz> (raw)
In-Reply-To: <CANEjr_Tspy0hyNgTQwL38X0jvcNUon_g2HMyoqZFQS+7e2qKow@mail.gmail.com>
On Tue, Mar 29, 2016 at 01:35:32AM +0530, Pradeep Jindal wrote:
> > > I am facing a weird problem, I earlier had a configuration wherein my
> > > backing device was a logical volume (LVM) backed by 3 software RAID0
> > > arrays having 2x1TB disks each, so totally 6TB of storage for backing
> > > device and 300GB logical volume (LVM) backed by SSD as a caching
> > > device. Both were configured as a cache set and I was getting around
> > > 84% cache hit ratio.
> > >
> > > Now, I have changed the backing device to a bare (no LVM, no raid) 6TB
> > > disk while everything else stays same (caching device on LVM, 300GB)
> > > and for exactly same workload I am only getting 58-60% cache hit
> > > ratio.
> > >
> > > I am confused, what could be the reason?
> >
> > Full stripe size writes are configured according to the backing device,
> > for example.
> Didn't quite get it, could you please elaborate?
Backing devices that advertise a stripe size cause bcache to enable a
mode where it tries to always write a full stripe to the backing
devices, hence changing behavior of the cache.
--
Vojtech Pavlik
Director SuSE Labs
next prev parent reply other threads:[~2016-03-28 20:19 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-28 18:17 84% -> 60% cache hit ratio for same workflow, different conf Pradeep Jindal
2016-03-28 19:17 ` Vojtech Pavlik
2016-03-28 20:10 ` Pradeep Jindal
[not found] ` <CANEjr_Tspy0hyNgTQwL38X0jvcNUon_g2HMyoqZFQS+7e2qKow@mail.gmail.com>
2016-03-28 20:19 ` Vojtech Pavlik [this message]
2016-03-28 20:22 ` Pradeep Jindal
[not found] ` <CANEjr_TWKkUB54rYOr84UmKXrGeJdN7c2z5Z-QerwNRT1Lz-9Q@mail.gmail.com>
2016-03-28 20:26 ` Pradeep Jindal
2016-03-29 6:02 ` Pradeep Jindal
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