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 linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
