From: Randy Dunlap <rdunlap@infradead.org>
To: Scott Bauer <scott.bauer@intel.com>, dm-devel@redhat.com
Cc: snitzer@redhat.com, agk@redhat.com, linux-kernel@vger.kernel.org,
keith.busch@intel.com, jonathan.derrick@intel.com
Subject: Re: [PATCH v3 2/2] dm unstripe: Add documentation for unstripe target
Date: Wed, 13 Dec 2017 16:18:06 -0800 [thread overview]
Message-ID: <808cd141-3c0a-d0ae-5b9d-efc19ab9f0fb@infradead.org> (raw)
In-Reply-To: <20171213213332.2914-3-scott.bauer@intel.com>
On 12/13/2017 01:33 PM, Scott Bauer wrote:
> Signed-off-by: Scott Bauer <scott.bauer@intel.com>
> ---
> Documentation/device-mapper/dm-unstripe.txt | 130 ++++++++++++++++++++++++++++
> 1 file changed, 130 insertions(+)
> create mode 100644 Documentation/device-mapper/dm-unstripe.txt
>
> diff --git a/Documentation/device-mapper/dm-unstripe.txt b/Documentation/device-mapper/dm-unstripe.txt
> new file mode 100644
> index 000000000000..01d7194b9075
> --- /dev/null
> +++ b/Documentation/device-mapper/dm-unstripe.txt
> @@ -0,0 +1,130 @@
> +Device-Mapper Unstripe
> +=====================
> +
[snip]
> +==============
> +
> +
> + Another example:
> +
> + Intel NVMe drives contain two cores on the physical device.
> + Each core of the drive has segregated access to its LBA range.
> + The current LBA model has a RAID 0 128k chunk on each core, resulting
> + in a 256k stripe across the two cores:
> +
> + Core 0: Core 1:
> + __________ __________
> + | LBA 512| | LBA 768|
> + | LBA 0 | | LBA 256|
> + ⎻⎻⎻⎻⎻⎻⎻⎻⎻⎻ ⎻⎻⎻⎻⎻⎻⎻⎻⎻⎻
Use ASCII characters ___ or ---, not whatever those bottom block characters are.
> +
> + The purpose of this unstriping is to provide better QoS in noisy
> + neighbor environments. When two partitions are created on the
> + aggregate drive without this unstriping, reads on one partition
> + can affect writes on another partition. This is because the partitions
> + are striped across the two cores. When we unstripe this hardware RAID 0
> + and make partitions on each new exposed device the two partitions are now
> + physically separated.
> +
> + With the module we were able to segregate a fio script that has read and
> + write jobs that are independent of each other. Compared to when we run
> + the test on a combined drive with partitions, we were able to get a 92%
> + reduction in five-9ths read latency using this device mapper target.
5/9ths
although I can't quite parse that sentence.
--
~Randy
next prev parent reply other threads:[~2017-12-14 0:18 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-13 21:33 [PATCH v3 0/2] dm-unstripe Scott Bauer
2017-12-13 21:33 ` [PATCH v3 1/2] dm-unstripe: unstripe RAID 0/dm-striped device Scott Bauer
2017-12-14 0:11 ` Randy Dunlap
2017-12-15 15:27 ` Scott Bauer
2017-12-15 19:55 ` Randy Dunlap
2017-12-13 21:33 ` [PATCH v3 2/2] dm unstripe: Add documentation for unstripe target Scott Bauer
2017-12-14 0:18 ` Randy Dunlap [this message]
2017-12-13 23:58 ` Scott Bauer
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