diff options
Diffstat (limited to 'Documentation/device-mapper/unstriped.rst')
-rw-r--r-- | Documentation/device-mapper/unstriped.rst | 135 |
1 files changed, 0 insertions, 135 deletions
diff --git a/Documentation/device-mapper/unstriped.rst b/Documentation/device-mapper/unstriped.rst deleted file mode 100644 index 0a8d3eb3f072..000000000000 --- a/Documentation/device-mapper/unstriped.rst +++ /dev/null @@ -1,135 +0,0 @@ -================================ -Device-mapper "unstriped" target -================================ - -Introduction -============ - -The device-mapper "unstriped" target provides a transparent mechanism to -unstripe a device-mapper "striped" target to access the underlying disks -without having to touch the true backing block-device. It can also be -used to unstripe a hardware RAID-0 to access backing disks. - -Parameters: -<number of stripes> <chunk size> <stripe #> <dev_path> <offset> - -<number of stripes> - The number of stripes in the RAID 0. - -<chunk size> - The amount of 512B sectors in the chunk striping. - -<dev_path> - The block device you wish to unstripe. - -<stripe #> - The stripe number within the device that corresponds to physical - drive you wish to unstripe. This must be 0 indexed. - - -Why use this module? -==================== - -An example of undoing an existing dm-stripe -------------------------------------------- - -This small bash script will setup 4 loop devices and use the existing -striped target to combine the 4 devices into one. It then will use -the unstriped target ontop of the striped device to access the -individual backing loop devices. We write data to the newly exposed -unstriped devices and verify the data written matches the correct -underlying device on the striped array:: - - #!/bin/bash - - MEMBER_SIZE=$((128 * 1024 * 1024)) - NUM=4 - SEQ_END=$((${NUM}-1)) - CHUNK=256 - BS=4096 - - RAID_SIZE=$((${MEMBER_SIZE}*${NUM}/512)) - DM_PARMS="0 ${RAID_SIZE} striped ${NUM} ${CHUNK}" - COUNT=$((${MEMBER_SIZE} / ${BS})) - - for i in $(seq 0 ${SEQ_END}); do - dd if=/dev/zero of=member-${i} bs=${MEMBER_SIZE} count=1 oflag=direct - losetup /dev/loop${i} member-${i} - DM_PARMS+=" /dev/loop${i} 0" - done - - echo $DM_PARMS | dmsetup create raid0 - for i in $(seq 0 ${SEQ_END}); do - echo "0 1 unstriped ${NUM} ${CHUNK} ${i} /dev/mapper/raid0 0" | dmsetup create set-${i} - done; - - for i in $(seq 0 ${SEQ_END}); do - dd if=/dev/urandom of=/dev/mapper/set-${i} bs=${BS} count=${COUNT} oflag=direct - diff /dev/mapper/set-${i} member-${i} - done; - - for i in $(seq 0 ${SEQ_END}); do - dmsetup remove set-${i} - done - - dmsetup remove raid0 - - for i in $(seq 0 ${SEQ_END}); do - losetup -d /dev/loop${i} - rm -f member-${i} - done - -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| - ---------- ---------- - -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 dm-unstriped target we're able to segregate an 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 read latency using this device mapper target. - - -Example dmsetup usage -===================== - -unstriped ontop of Intel NVMe device that has 2 cores ------------------------------------------------------ - -:: - - dmsetup create nvmset0 --table '0 512 unstriped 2 256 0 /dev/nvme0n1 0' - dmsetup create nvmset1 --table '0 512 unstriped 2 256 1 /dev/nvme0n1 0' - -There will now be two devices that expose Intel NVMe core 0 and 1 -respectively:: - - /dev/mapper/nvmset0 - /dev/mapper/nvmset1 - -unstriped ontop of striped with 4 drives using 128K chunk size --------------------------------------------------------------- - -:: - - dmsetup create raid_disk0 --table '0 512 unstriped 4 256 0 /dev/mapper/striped 0' - dmsetup create raid_disk1 --table '0 512 unstriped 4 256 1 /dev/mapper/striped 0' - dmsetup create raid_disk2 --table '0 512 unstriped 4 256 2 /dev/mapper/striped 0' - dmsetup create raid_disk3 --table '0 512 unstriped 4 256 3 /dev/mapper/striped 0' |