I replaced the SSD intent log drive with an NVME drive, and the system is much more stable now.
*David Johnson* *Director of Development, Maxis Technology* 844.696.2947 ext 702 (o) | 479.531.3590 (c) <https://www.linkedin.com/in/pojoguy/> <https://maxistechnology.com/wp-content/uploads/vcards/vcard-David_Johnson.vcf> <https://maxistechnology.com/> *Follow us:* <https://www.linkedin.com/company/maxis-tech-inc/> On Thu, May 27, 2021 at 5:57 PM David Johnson <djohn...@maxistechnology.com> wrote: > Hi ovirt gurus, > > This is an interesting issue, one I never expected to have. > > When I push high volumes of writes to my NAS, I will cause VM's to go into > a paused state. I'm looking at this from a number of angles, including > upgrades on the NAS appliance. > > I can reproduce this problem at will running a centos 7.9 VM on Ovirt 4.5. > > *Questions:* > > 1. Is my analysis of the failure (below) reasonable/correct? > > 2. What am I looking for to validate this? > > 3. Is there a configuration that I can set to make it a little more robust > while I acquire the hardware to improve the NAS? > > > *Reproduction:* > > Standard test of file write speed: > > [root@cen-79-pgsql-01 ~]# dd if=/dev/zero of=./test bs=512k count=4096 > oflag=direct > 4096+0 records in > 4096+0 records out > 2147483648 bytes (2.1 GB) copied, 1.68431 s, 1.3 GB/s > > > Give it more data > > [root@cen-79-pgsql-01 ~]# dd if=/dev/zero of=./test bs=512k count=12228 > oflag=direct > 12228+0 records in > 12228+0 records out > 6410993664 bytes (6.4 GB) copied, 7.22078 s, 888 MB/s > > > The odds are about 50/50 that 6 GB will kill the VM, but 100% when I hit 8 > GB. > > *Analysis:* > > What I think appears to be happening is that the intent cache on the NAS > is on an SSD, and my VM's are pushing data about three times as fast as the > SSD can handle. When the SSD gets queued up beyond a certain point, the NAS > (which places reliability over speed) says "Whoah Nellie!", and the VM > chokes. > > > *David Johnson* >
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