Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On Thu, Feb 2, 2012 at 9:23 AM, Lars Ellenberg <lars.ellenberg at linbit.com> wrote: > On Wed, Feb 01, 2012 at 08:46:54PM -0430, Jose Ildefonso Camargo Tolosa wrote: >> Greetings, >> >> I'm doing some experimentation with DRBD and relatively low speed >> links (~30Mbps), with latency around 34ms. I have this: >> >> 1. DRBD version: 8.3.7 (api:88/proto:86-91) >> 2. Several virtual machine images on the DRBD volume. >> 3. deadline scheduler by default. >> 4. LVM on top of DRBD, and ext4 on top of this LVM. >> >> I did this: >> >> 1. I started 3 KVM VMs (mainly idle). >> 2. I started to copy a big file (50GB) into DRBD partition. >> 3. I started to use the VMs, mainly read-only operations, with some >> small writes. >> >> At some point, the VMs just froze while trying to read. So, I went to >> physical machine, and tried a "ls" on a directory inside the DRBD >> volume, that I hasn't saw before (so it was not cached)... ls command >> also froze.... access to cached data seems to be unaffected, then, I >> stopped the cp process (ctrl-z), and waited for network traffic to >> stop (patiently watching bwm). After network (replication) traffic >> stopped: all unfroze. >> >> Now, my understanding is that DRBD reads are local, and thus: I can't >> understand why writing would freeze the reads.... >> >> Any ideas? > > Try the same without DRBD, I would expect similar effects. > I suspect your are simply overloading your IO subsystem. I already did that, before posting to the list. Also, note that the problem doesn't happen if I disconnect the secondary.