Dne 7.11.2016 v 10:30 Alexander 'Leo' Bergolth napsal(a):
Hi!
I am experiencing a dramatic degradation of the sequential write speed
on a raid1 LV that resides on two USB-3 connected harddisks (UAS
enabled), compared to parallel access to both drives without raid or
compared to MD raid:
- parallel sequential writes LVs on both disks: 140 MB/s per disk
- sequential write to MD raid1 without bitmap: 140 MB/s
- sequential write to MD raid1 with bitmap: 48 MB/s
- sequential write to LVM raid1: 17 MB/s !!
According to the kernel messages, my 30 GB raid1-test-LV gets equipped
with a 61440 bit write-intent bitmap (1 bit per 512 byte data?!) whereas
a default MD raid1 bitmap only has 480 bit size. (1 bit per 64 MB).
Maybe the dramatic slowdown is caused by this much too fine grained
bitmap and its updates, which are random IO?
Is there a way to configure the bitmap size?
Hi
Can you please provide some results with '--regionsize' changes ?
While '64MB' is quite 'huge' for resync I guess 'the current' default
picked region size is likely very very small in same cases.
Regards
Zdenek
_______________________________________________
linux-lvm mailing list
[email protected]
https://www.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
