I create a *4x256GB-SSD RAID0(/dev/md1)* and I test the performance through fio. fio config:
ioengine=libaiodirect=1time_basedruntime=120ramp_time=30size=100g The sequential read/write performance is: > > *read: 2000MB/swrite: 1800MB/s* Now I make a ext4 on the RAID0(/dev/md1) and mount on /home/. ANd I create a 100G-disk.qcow2 by guestfish. > $guestfish > ><fish>: disk-create disk.qcow2 qcow2 100*1024*1024*1024 > ><fish>: run > ><fish>: mkfs ext4 /dev/sda > ><fish>: shutdown > ><fish>: quit No errors showed. I mount the disk.qcow2 on the /home/test/, and create a 50GB file. > $dd if=/dev/zero of=/home/test/file bs=1M count=51280 Test sequential read/write again through fio and config almost the same: ioengine=libaiodirect=1time_basedruntime=120ramp_time=30size=50g and the testing filename is /home/test/file and the performance is : > > *read: 86MB/swrite: 43MB/s* how come the performance is so bad? almost down 95%. My machine is: 4.4.0-83-generic, Ubuntu 16.04, x86_64 GNU/Linux
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