Hi All, Just a heads up after a day’s experimentation. I believe tgt with its default settings has a small write cache when exporting a kernel mapped RBD. Doing some write tests I saw 4 times the write throughput when using tgt aio + krbd compared to tgt with the builtin librbd. After running the following command against the LUN, which apparently disables write cache, Performance dropped back to what I am seeing using tgt+librbd and also the same as fio. tgtadm --op update --mode logicalunit --tid 2 --lun 3 -P mode_page=8:0:18:0x10:0:0xff:0xff:0:0:0xff:0xff:0xff:0xff:0x80:0x14:0:0:0:0:0:0 From that I can only deduce that using tgt + krbd in its default state is not 100% safe to use, especially in an HA environment. Nick |
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