Hello, after deploying reflink-based VM snapshots to production servers we discovered a performace degradation:
OS: Opensuse 13.1, 13.2 Hypervisors: Xen 4.4, 4.5 Dom0 kernels: 3.12, 3.16, 3.18 DomU kernels: 3.12, 3.16, 3.18 Tested DomU disk backends: tapdisk2, qdisk 1) on DomU (VM) #dd if=/dev/zero of=test2 bs=1M count=6000 2) atop on Dom0: sdb - busy:92% - read:375 - write:130902 Reads are from others VMs, seems OK 3) DomU dd finished: 6291456000 bytes (6.3 GB) copied, 16.6265 s, 378 MB/s 4) Lets start dd again & do a snapshot: #dd if=/dev/zero of=test2 bs=1M count=6000 #reflink test.raw ref/ 5) atop on Dom0: sdb - busy:97% - read:112740 - write:28037 So, Read IOPS = 112740, why? 6) DomU dd finished: 6291456000 bytes (6.3 GB) copied, 175.45 s, 35.9 MB/s 7) Second & further reflinks do not change the atop stat & dd time #dd if=/dev/zero of=test2 bs=1M count=6000 #reflink --backup=t test.raw ref/ \\ * n times ~ 6291456000 bytes (6.3 GB) copied, 162.959 s, 38.6 MB/s The question is why reflinking a running VM disk leads to read IOPS storm? Thanks! -- Best regards, Eugene Istomin _______________________________________________ Ocfs2-devel mailing list Ocfs2-devel@oss.oracle.com https://oss.oracle.com/mailman/listinfo/ocfs2-devel
