Thank you very much for your answer. I am copying ovirt-devel too as that could be of interest to them.
Guillaume Pavese Ingénieur Système et Réseau Interactiv-Group On Sat, Mar 2, 2019 at 7:00 AM Michael Sclafani <sclaf...@redhat.com> wrote: > Hi! > > 512 emulation was intended to support drivers that only do a fraction of > their I/O in blocks smaller 4KB. It is not optimized for performance in any > way. Under the covers, VDO is still operating on 4KB physical blocks, so > each 512-byte read is potentially amplified to a 4KB read, and each > 512-byte write to a 4KB read followed by a 4KB write. A workload consisting > exclusively of 512-byte randomly-distributed writes could effectively be > amplified by a factor of 16. > > We have a suite of automated tests we run in 512e mode on a nightly basis. > That suite is a subset of our regular tests, containing only ones we expect > would be likely to expose problems specific to the emulation. > > There should be no penalty to having emulation enabled on a volume that no > longer uses it. If the I/O is 4KB-aligned and 4KB or larger, having it > enabled won't affect it. > It does not appear the setting can be modified by the VDO manager, but I > cannot remember at this moment why that should be so. > > Hope this helps. > > On Fri, Mar 1, 2019 at 2:24 PM Guillaume Pavese < > guillaume.pav...@interactiv-group.com> wrote: > >> Hello, >> >> We are planning to deploy VDO with oVirt 4.3 on centos 7.6 (on SSD >> devices). >> As oVirt does not support 4K devices yet, VDO volumes are created with >> the parameter "--emulate512 enabled" >> >> What are the implications of this setting? Does it impact performance? If >> so, is it IOPS or throughput that is impacted? What about reliability (is >> that mode equally tested as standard mode)? >> >> As I saw on RH Bugzilla, support for 4K devices in oVirt will need to >> wait at least for Centos 7.7 >> Once that is supported, would it be possible to transition/upgrade an >> emulate512 vdo volume to a standard one? >> >> Thanks, >> >> Guillaume Pavese >> Ingénieur Système et Réseau >> Interactiv-Group >> _______________________________________________ >> Vdo-devel mailing list >> vdo-de...@redhat.com >> https://www.redhat.com/mailman/listinfo/vdo-devel >> >
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