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On 03.10.2018 20:10, jesper@xxxxxxxx
wrote:
Your use case sounds it might profit from the rados cache tier feature. It's a rarely used feature because it only works in very specific circumstances. But your scenario sounds like it might work. Definitely worth giving it a try. Also, dm-cache with LVM *might* help. But if your active working set is really just 400GB: Bluestore cache should handle this just fine. Don't worry about "unequal" distribution, every 4mb chunk of every file will go to a random OSD.I tried it out - and will do it more but Initial tests didnt really convince me - but I'll try more.One very powerful and simple optimization is moving the metadata pool to SSD only. Even if it's just 3 small but fast SSDs; that can make a huge difference to how fast your filesystem "feels".They are ordered and will hopefully arrive very soon. Can I: 1) Add disks 2) Create pool 3) stop all MDS's 4) rados cppool 5) Start MDS .. Yes, thats a cluster-down on CephFS but shouldn't take long. Or is there a better guide? this post https://ceph.com/community/new-luminous-crush-device-classes/ and this document http://docs.ceph.com/docs/master/rados/operations/pools/ explains how the osd class is used to define a crush placement rule. and then you can set the crush_rule on the pool and ceph will
move the data. No downtime needed. kind regards Ronny Aasen |
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