Hi, I have a workstation which runs Fedora 21 with linux-3.19 kernel and create a thin pool onto of a RAID0 (chunksize = 512KB) with five Crucial 256GB SSDs. [root@localhost ~]# dmsetup create pool --table "0 2478300160 thin-pool /dev/md0p1 /dev/md0p2 1024 0 1 skip_block_zeroing" Then, I create a small thin volume with the following commands. [root@localhost ~]# dmsetup message pool 0 "create_thin 0" [root@localhost ~]# dmsetup create thin --table "0 400000000 thin /dev/mapper/pool 0" After that, I use both dd and fio for throughput testing and get the following result. [root@localhost ~]# dd if=/dev/zero of=/dev/mapper/thin bs=2M count=25k 25600+0 records in 25600+0 records out 53687091200 bytes (54 GB) copied, 29.0871 s, 1.8 GB/s The 1.8 GB/s throughput looks pretty reasonable to me. However, after taking a single snapshot of this thin device, I get a pretty low throughput with the same command. [root@localhost ~]# dd if=/dev/zero of=/dev/mapper/thin bs=2M count=25k 25600+0 records in 25600+0 records out 53687091200 bytes (54 GB) copied, 191.495 s, 280 MB/s I am aware of that writing to a snapshotted device will trigger lots of copy-on-write requests, so I was expecting a 50~60% performance loss in this case. However, 85% performance loss can be observed in my test above. Am I doing anything wrong or is there anything I can tune to make this right? If someone can point direction for me, I am glad to test or even modify the source code to solve this case. Thanks, Dennis -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel