[OmniOS-discuss] Zil Device

[Andrew Gabriel]

On 16/07/2015 19:38, Richard Elling wrote:
>
>> On Jul 16, 2015, at 11:30 AM, Schweiss, Chip <chip at innovates.com 
>> <mailto:chip at innovates.com>> wrote:
>>
>> The 850 Pro should never be used as a log device.  It does not have 
>> power fail protection of its ram cache.   You might as well set 
>> sync=disabled and skip using a log device entirely because the 850 
>> Pro is not protecting your last transactions in case of power failure.
>
> Chip, are you asserting that the 850 Pro does not honor the cache 
> flush command?
> In the bad old days, there were SSDs that were broken for cache 
> flushes, but some of
> the most important (to Samsung) OSes, like Windows, rely on cache 
> flushes to work.
> ZFS does as well.
>  -- richard

Was just in the middle of writing something similar when your reply came in.
Just to add, ZIL devices don't have to have power fail emergency supply 
to work correctly.
What's important is that they don't lie about when they get data to 
non-volatile storage.
Those with power fail protection can in many cases reply when data hits 
their DRAM cache, whereas those without have to wait a bit longer until 
the data hits the flash chips. So the difference tends to impact latency 
of synchronous operations, but in both cases they are very much faster 
than waiting until the data hits the platters of spinning rust.

-- 
Andrew Gabriel
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://omniosce.org/ml-archive/attachments/20150716/f7d5af19/attachment.html>