Re: [dm-devel] [PATCH v2] staging: writeboost: Add dm-writeboost
From: Bart Van Assche
Date: Fri Dec 12 2014 - 04:12:33 EST
On 12/12/14 01:42, Akira Hayakawa wrote:
1. Writeboost shouldn't split the bio into 4KB chunks.
No. It is necessary.
I know WALB (https://github.com/starpos/walb) logs data without
splitting but the data structure becomes complicated.
If you read my code carefully, you will notice that splitting
helps the design simplicity and performance.
This is the first time I see someone claiming that reducing the request
size improves performance. I don't know any SSD model for which
splitting requests improves performance.
Additionally, since bio's are split by dm-writeboost, this makes me
wonder how atomic writes will ever be supported ? Atomic writes are
being standardized by the T10 SCSI committee. I don't think the Linux
block layer already supports atomic writes today but I expect support
for atomic writes to be added to the block layer sooner or later. See
e.g. http://www.t10.org/doc13.htm / SBC-4 SPC-5 Atomic writes and reads
for the latest draft specification.
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