[sheepdog-users] Puzzled about bad performances

Vasiliy Tolstov v.tolstov at selfip.ru
Thu May 21 10:32:01 CEST 2015

2015-05-21 4:06 GMT+03:00 Hitoshi Mitake <mitake.hitoshi at gmail.com>:
> In a case of write, I'm not sure that improving performance with
> caching without sacrificing durability is possible or not. Because
> OSes and applications do their best for minimizing disk flush. So
> cached data in virtual block devices would tend not to be dirty. It
> means effectiveness of the caching is not so good.
> Actually, many proprietary storage appliances seem to employ NVRAM or
> other flash devices for write caching (e.g. Nimble Storage
> http://www.nimblestorage.com/products-technology/casl-architecture/)
> These sort of storages reply ack to write request after storing the
> data in their cache, not disk. I dont' know anything detail about
> the architecture. But it seems to be degrading durability temporally.

In this case something like bcache can get more performance, bacuse
its write to ssd and after some time data goes to hdd.
If power failure after reboot data from ssd applied to hdd first. But
this is not the safest solution...

Vasiliy Tolstov,
e-mail: v.tolstov at selfip.ru

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