On 11/07/2016 11:22 AM, Zdenek Kabelac wrote: > Dne 7.11.2016 v 10:30 Alexander 'Leo' Bergolth napsal(a): >> 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? > > 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. Ah - thanks. Didn't know that --regionsize is also valid for --type raid1. With --regionsize 64 MB, the bitmap has the same size as the default bitmap created by mdadmin and write performance is also similar: *** --regionsize 1M 1048576000 bytes (1,0 GB, 1000 MiB) copied, 63,957 s, 16,4 MB/s *** --regionsize 2M 1048576000 bytes (1,0 GB, 1000 MiB) copied, 39,1517 s, 26,8 MB/s *** --regionsize 4M 1048576000 bytes (1,0 GB, 1000 MiB) copied, 32,8275 s, 31,9 MB/s *** --regionsize 16M 1048576000 bytes (1,0 GB, 1000 MiB) copied, 30,2903 s, 34,6 MB/s *** --regionsize 32M 1048576000 bytes (1,0 GB, 1000 MiB) copied, 30,1452 s, 34,8 MB/s *** --regionsize 64M 1048576000 bytes (1,0 GB, 1000 MiB) copied, 21,6208 s, 48,5 MB/s *** --regionsize 128M 1048576000 bytes (1,0 GB, 1000 MiB) copied, 14,2028 s, 73,8 MB/s *** --regionsize 256M 1048576000 bytes (1,0 GB, 1000 MiB) copied, 11,6581 s, 89,9 MB/s Is there a way to change the regionsize for an existing LV? Cheers, --leo -- e-mail ::: Leo.Bergolth (at) wu.ac.at fax ::: +43-1-31336-906050 location ::: IT-Services | Vienna University of Economics | Austria _______________________________________________ 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/
