On 6/30/2010 7:17 PM, Fred Liu wrote:
> See. Thanks.
> Does it have the hardware functionality to detect the power outage and do
> force cache flush when the cache is enabled?
> Any more detailed info about the capacity (farad) of this supercap and how
> long one discharge will be?
I don't think it matters the actual size of the supercap. As Bob said,
it only needs to be sized to be big enough to allow all on-board DRAM to
be flushed out to Flash. How big that should be is easily determined by
the manufacturer, and they'd be grossly negligent if it wasn't at least
that size. Any capacity beyond that needed to do a single full flush is
excess, so I would hazard a guess that the supercap is "just big enough,
and no more". That is, just enough to power the SSD for the partial
second or so it takes to flush to flash. I don't think we need to worry
how big that actually is.
Answering your second question first - my reading of the info is that it
will force a cache flush (if the cache is enabled) upon loss of power
under any circumstance. That is, it will flush the cache in both a
controlled power-down (regardless of whether the OS says to do so) and
in an immediate power loss. All this is in the SSD's firmware.
> -----Original Message-----
> From: Bob Friesenhahn [mailto:bfriesen@xxxxxxxxxxxxxxxxxxx]
> Sent: 星期四, 七月 01, 2010 10:01
> To: Fred Liu
> Cc: 'OpenSolaris ZFS discuss'
> Subject: Re: [zfs-discuss] OCZ Vertex 2 Pro performance numbers
> On Wed, 30 Jun 2010, Fred Liu wrote:
>> Any duration limit on the supercap? How long can it sustain the data?
> A supercap on a SSD drive only needs to sustain the data until it has
> been saved (perhaps 10 milliseconds). It is different than a RAID
> array battery.
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