The problem is related to inconsistent io hinting semantics:
minimum io size = preferred random io size.
optimal io size = preferred streaming io size.
For a RAID this would be chunk and stripe sizes and you certainly want
your first PE stripe aligned. On the other hand, in your example (usb
attached drive by any chance?) the prefferred streaming io size is not
relevant for alignment.
IMHO this needs to be rectified by cleary stating the semantics on IO
hinting.
Regards
-Sven
Am 27.11.2016 um 19:52 schrieb Alexander 'Leo' Bergolth:
Hi!
I noticed that a newly created PV on a 512k sector SATA disk uses a PE
alignment of 65535, which seems rather strange...
# pvs -o +pe_start --units s
PV VG Fmt Attr PSize PFree 1st PE
/dev/sda2 vg_sys lvm2 a-- 117211136S 45907968S 2048S
/dev/sdb1 lvm2 --- 3221225472S 3221225472S 65535S
/dev/sde1 vg_data lvm2 a-- 1953513472S 879771648S 2048S
Looking at the verbose output of pvcreate, this seems to be derived from
/sys/block/sdb/queue/optimal_io_size:
# grep . /sys/block/sdb/queue/*size
/sys/block/sdb/queue/hw_sector_size:512
/sys/block/sdb/queue/logical_block_size:512
/sys/block/sdb/queue/max_segment_size:4096
/sys/block/sdb/queue/minimum_io_size:4096
/sys/block/sdb/queue/optimal_io_size:33553920
/sys/block/sdb/queue/physical_block_size:512
I can manually set a correct value of dataalignment of course.
However, shouldn't lvm assure that PE alignment is set to a multiple of
the minimum_io_size?
Cheers,
--leo
I am using lvm2-2.02.130-5.el7_2.5.x86_64
This is the disk:
Disk /dev/sdb: 5860533168 sectors, 2.7 TiB
Logical sector size: 512 bytes
Disk identifier (GUID): D28E3352-7CE6-4AAB-802A-59270088604E
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 5860533134
Partitions will be aligned on 2048-sector boundaries
Total free space is 2639307629 sectors (1.2 TiB)
Number Start (sector) End (sector) Size Code Name
1 2048 3221227519 1.5 TiB 8E00 Linux LVM
# sg_inq -p 0xb0 /dev/sdb
VPD INQUIRY: Block limits page (SBC)
Maximum compare and write length: 0 blocks
Optimal transfer length granularity: 8 blocks
Maximum transfer length: 65535 blocks
Optimal transfer length: 65535 blocks
Maximum prefetch, xdread, xdwrite transfer length: 65535 blocks
Maximum unmap LBA count: 0
Maximum unmap block descriptor count: 0
Optimal unmap granularity: 0
Unmap granularity alignment valid: 0
Unmap granularity alignment: 0
# pvcreate -vv /dev/sdb1
Setting activation/monitoring to 1
Setting global/locking_type to 1
Setting global/wait_for_locks to 1
File-based locking selected.
Setting global/prioritise_write_locks to 1
Setting global/locking_dir to /run/lock/lvm
Setting global/use_lvmlockd to 0
metadata/pvmetadataignore not found in config: defaulting to 0
metadata/pvmetadatasize not found in config: defaulting to 255
metadata/pvmetadatacopies not found in config: defaulting to 1
Locking /run/lock/lvm/P_orphans WB
Setting response to OK
Setting response to OK
Setting id to Atul0q-kVgc-yptP-NAbb-ulm9-zx8l-bu8cei
Setting vgid to xhIC4u-hJk7-hR0y-1nvw-wJal-wRbz-gYuICd
Setting vgname to vg_data
Setting format to lvm2
Setting device to 2113
Setting dev_size to 1000202771968
Setting label_sector to 1
Setting size to 1044480
Setting start to 4096
Setting ignore to 0
Setting id to 0d3kX3-SnUS-eKfx-M47m-rQFG-50DV-apC1d6
Setting vgid to uRefqt-U56B-c343-q7DS-DDtt-m3Wz-nVnihu
Setting vgname to vg_sys
Setting format to lvm2
Setting device to 2050
Setting dev_size to 60014075392
Setting label_sector to 1
Setting size to 1044480
Setting start to 4096
Setting ignore to 0
Setting response to OK
Setting response to OK
Setting name to vg_sys
Setting metadata/format to lvm2
Setting id to 0d3kX3-SnUS-eKfx-M47m-rQFG-50DV-apC1d6
Setting format to lvm2
Setting device to 2050
Setting dev_size to 117214991
Setting label_sector to 1
Found same device /dev/sda2 with same pvid
0d3kX3SnUSeKfxM47mrQFG50DVapC1d6
Setting size to 1044480
Setting start to 4096
Setting ignore to 0
Setting response to OK
Setting response to OK
Setting response to OK
Setting response to OK
Setting name to vg_data
Setting metadata/format to lvm2
Setting id to Atul0q-kVgc-yptP-NAbb-ulm9-zx8l-bu8cei
Setting format to lvm2
Setting device to 2113
Setting dev_size to 1953521039
Setting label_sector to 1
Found same device /dev/sde1 with same pvid
Atul0qkVgcyptPNAbbulm9zx8lbu8cei
Setting size to 1044480
Setting start to 4096
Setting ignore to 0
Setting response to OK
Setting response to OK
/dev/sdb1: size is 3221225472 sectors
/dev/sdb1: size is 3221225472 sectors
Setting allocation/use_blkid_wiping to 1
/dev/sdb1: size is 3221225472 sectors
/dev/sdb1: size is 3221225472 sectors
/dev/sdb1: size is 3221225472 sectors
Setting devices/data_alignment to 0
devices/default_data_alignment not found in config: defaulting to 1
Setting devices/md_chunk_alignment to 1
Setting devices/data_alignment_detection to 1
Device /dev/sdb1: queue/minimum_io_size is 4096 bytes.
Device /dev/sdb1: queue/optimal_io_size is 33553920 bytes.
/dev/sdb1: Setting PE alignment to 65535 sectors.
Setting devices/data_alignment_offset_detection to 1
Device /dev/sdb1: alignment_offset is 0 bytes.
/dev/sdb1: Setting PE alignment offset to 0 sectors.
Set up physical volume for "/dev/sdb1" with 3221225472 available sectors
Scanning for labels to wipe from /dev/sdb1
Zeroing start of device /dev/sdb1
Writing physical volume data to disk "/dev/sdb1"
/dev/sdb1: Writing label to sector 1 with stored offset 32.
Setting response to OK
Setting response to OK
Physical volume "/dev/sdb1" successfully created
Unlocking /run/lock/lvm/P_orphans
_______________________________________________
linux-lvm mailing list
linux-lvm@redhat.com
https://www.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
