On 11.12.2017 18:00, Scott Bauer wrote: > Signed-off-by: Scott Bauer <scott.bauer@xxxxxxxxx> > --- > Documentation/device-mapper/dm-unstripe.txt | 82 +++++++++++++++++++++++++++++ > 1 file changed, 82 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..4e1a0a39a689 > --- /dev/null > +++ b/Documentation/device-mapper/dm-unstripe.txt > @@ -0,0 +1,82 @@ > +Device-Mapper Unstripe > +===================== > + > +The device-mapper Unstripe (dm-unstripe) target provides a transparent > +mechanism to unstripe a RAID 0 striping to access segregated disks. > + > +This module should be used by users who understand what the underlying > +disks look like behind the software/hardware RAID. > + > +Parameters: > +<drive (ex: /dev/nvme0n1)> <drive #> <# of drives> <stripe sectors> > + > + > +<drive> > + The block device you wish to unstripe. > + > +<drive #> > + The physical drive you wish to expose via this "virtual" device > + mapper target. This must be 0 indexed. > + > +<# of drives> > + The number of drives in the RAID 0. > + > +<stripe sectors> > + The amount of 512B sectors in the raid striping, or zero, if you > + wish you use max_hw_sector_size. > + > + > +Why use this module? > +===================== > + > +As a use case: > + > + > + As an 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 stripe across the two cores: > + > + Core 0: Core 1: > + __________ __________ > + | LBA 511| | LBA 768| > + | LBA 0 | | LBA 256| > + ⎻⎻⎻⎻⎻⎻⎻⎻⎻⎻ ⎻⎻⎻⎻⎻⎻⎻⎻⎻⎻ If it's 128k stripe shouldn't it be LBAs 0/256 on core0 and LBAs 128/511 on core1? > + > + 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. With the striping concurrent > + reads and writes and I/O on opposite cores have lower completion times, > + and better tail latencies. > + > + 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. > + > + > + One could use the module to Logical de-pop a HDD if you have sufficient > + geometry information regarding the drive. > + > + > +Example scripts: > +==================== > + > +dmsetup create nvmset1 --table '0 1 dm-unstripe /dev/nvme0n1 1 2 0' > +dmsetup create nvmset0 --table '0 1 dm-unstripe /dev/nvme0n1 0 2 0' > + > +There will now be two mappers: > +/dev/mapper/nvmset1 > +/dev/mapper/nvmset0 > + > +that will expose core 0 and core 1. > + > + > +In a Raid 0 with 4 drives of stripe size 128K: > +dmsetup create raid_disk0 --table '0 1 dm-unstripe /dev/nvme0n1 0 4 256' > +dmsetup create raid_disk1 --table '0 1 dm-unstripe /dev/nvme0n1 1 4 256' > +dmsetup create raid_disk2 --table '0 1 dm-unstripe /dev/nvme0n1 2 4 256' > +dmsetup create raid_disk3 --table '0 1 dm-unstripe /dev/nvme0n1 3 4 256' > + > -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
