On 12/13/2017 01:33 PM, Scott Bauer wrote: > Signed-off-by: Scott Bauer <scott.bauer@xxxxxxxxx> > --- > 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 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
