On Tue, Apr 14, 2020 at 08:15:15PM +0200, Rainer Krienke wrote: > Am 14.04.20 um 18:09 schrieb Alwin Antreich: > > >> > >> In a VM I also tried to read its own striped LV device: dd > >> if=/dev/vg/testlv of=/dev/null bs=1024k status=progress (after clearing > >> the VMs cache). /dev/vg/testlv is a striped LV (on 4 disks) with xfs on > >> it on which I tested the speed using bonnie++ before. > >> This dd also did not go beyond about 100MB/sec, whereas the rados bench > >> promises much more. > > Do you have a VM without stripped volumes? I suppose there will be two > > requests, for each half of the data. That could slow down the read as> well. > > Yes the logical volume is striped using 4 physical volumes (RBDs). But > since exactly this setup helped to boost up writing (more paralellism) > it should do exactly the same since blocks can be read from more > separate rbd devices and thus more disks in general. > > I also tested a VM with just a single rbd used for the VMs disk and > there the effect ist quite the same. > > > > > And you can disable the cache to verify that cache misses don't impact > > the performance. > > I tried and disabled the writeback cache but the effect was only minimal. It seems that at this point the optimizations need to be done inside the VM (eg. readahead). I think the data that is requested is not in the cache and to small to be done within one read operation.
-- Cheers, Alwin _______________________________________________ pve-user mailing list firstname.lastname@example.org https://pve.proxmox.com/cgi-bin/mailman/listinfo/pve-user