Hi, I've been trying to benchmark a new System and currently have trouble understanding the numbers I'm seeing. The System is equipped with an LSI 9266-8i dual-core controller with 1G cache. This controller is configured with two logical drives: one 4 sas disk raid5 and one 3 Intel 320 SSD disk raid5. Initial fio benchmarking with the folling config: [randwrite] rw=randwrite direct=1 filename=/dev/vg_test/lv_benchmark numjobs=1 group_reporting bs=4k runtime=300 led to these results for the two volumes: sas: write: io=141368KB, bw=482529 B/s, iops=117 , runt=300004msec ssd: write: io=2799.5MB, bw=9555.5KB/s, iops=2388 , runt=300001msec (notice that I set the caching policy to writethrough for both logical drives) Next I create a KVM virtual machine with MongoDB on the system and created a small system drive and one sas and one ssd drive for the data and used them for the virtual machine. When I now run an looped inserts on the database I can get 23.000 inserts with the sas disks but only 3000 inserts with the ssd disks? What is really puzzling is that the IOPS numbers monitored look really strange. In the sas case I see around 100 iops which seems a little low but the inserted record is about 250 bytes in size so this might be explained by MongoDB submitting multiple records with one IOP? But when I use the SSD raid5 instead I see 3000 iops on the hosts (and in the guest). I have no explanation for this. Why would the number of iops be so different especially in the guest that cannot even see the difference because the disk is only presented as an abstrakt virtio disk to it? Does anyone have an idea why the SSD disks perform so dramatically worse than the SAS disks? Regards, Dennis -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
