Hi,
On 09/20/2017 11:10 AM, Sam Huracan wrote:
So why do not journal write only metadata?
As I've read, it is for ensure consistency of data, but I do not know
how to do that in detail? And why BlueStore still ensure consistency
without journal?
The main reason for having a journal with filestore is having a block
device that supports synchronous writes. Writing to a filesystem in a
synchronous way (e.g. including all metadata writes) results in a huge
performance penalty.
With bluestore the data is also stored on a block devices, and thus also
allows to perform synchronous writes directly (given the backing storage
is handling sync writes correctly and in a consistent way, e.g. no drive
caches, bbu for raid controllers/hbas). And similar to the filestore
journal the bluestore wal/rocksdb partitions can be used to allow both
faster devices (ssd/nvme) and faster sync writes (compared to spinners).
Regards,
Burkhard
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