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Hi,
On 07/22/13 06:05, Charles 'Boyo wrote: Secondly, I'm unclear about how OSDs use the journal. It appears they write to the journal (in all cases, can't be turned off), ack to the client and then read the journal later to write to backing storage. Is that correct? Yes I'm coming from enterprise ZFS with an SSD is also used for write journalling but data flushes are from the disk cache in memory, hence the use of write optimized SSDs. Why can't Ceph be configured to write from RAM instead of reading the journal on flush? From my stats I can tell that the journal flushes use the kernel's cache and do not hit the SSD. Here, sdd is my journal SSD :  |
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