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On 04/18/17 11:44, Jogi Hofmüller
wrote:
The well known fact part was CoW which I guess is for all versions.Hi, Am Dienstag, den 18.04.2017, 13:02 +0200 schrieb mj:On 04/18/2017 11:24 AM, Jogi Hofmüller wrote:This might have been true for hammer and older versions of ceph. From what I can tell now, every snapshot taken reduces performance of the entire cluster :(Really? Can others confirm this? Is this a 'wellknown fact'? (unknown only to us, perhaps...)I have to add some more/new details now. We started removing snapshots for VMs today. We did this VM for VM and waited some time in between while monitoring the cluster. After having removed all snapshots for the third VM the cluster went back to a 'normal' state again: no more slow requests. i/o waits for VMs are down to acceptable numbers again (<10% peeks, <5% average). So, either there is one VM/image that irritates the entire cluster or we reached some kind of threshold or it's something completely different. As for the well known fact: Peter Maloney pointed that out in this thread (mail from last Thursday). The 'slower with every snapshot even after CoW totally flattens it' issue I just find easy to test, and I didn't test it on hammer or earlier, and others confirmed it, but didn't keep track of the versions. Just make an rbd image, map it (probably... but my tests were with qemu librbd), do fio randwrite tests with sync and direct on the device (no need for a fs, or anything), and then make a few snaps and watch it go way slower. How about we make this thread a collection of versions then. And I'll redo my test on Thursday maybe. Regards,
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