I admit I haven't studied the patches. Anyway, here is what I have to
say about what I (mis?)understood from your posts:
James Smart wrote:
You need to be careful on the power-up. Many JBODs share a single
"enclosure" and that enclosure has a limited power supply. If all
drives were spun up in parallel (and a drive may take 10-15seconds
to spin up), then they can overload the enclosure's power limit.
[...]
There were not a lot of great answers on how to solve this as it usually
required knowledge of how the hardware was packaged.
[...]
On Thu, Sep 29, 2005 at 08:34:37AM +0100, Christoph Hellwig wrote:
is an ULDD operation, not an LLDD one, and this fits the layering model
much better.
The operation _involves_ the high level, yes. But whether it may be/
must not be performed has to be controlled by the transport layer. Take
FireWire as an example: IEEE 1394(a,b) has power management
specifications. (NB: Its indeed in IEEE 1394, not in the SBP-2 spec.)
One rule is that only one node on a FireWire bus may perform power
management; the node which is allowed to do this is determined by a
special protocol.
Actually one important thing is missing, that is a way to avoid spinning
down external disks. As a start a sysfs-controlable flag should do it,
later we can add transport-specific ways to find out whether a device
is external.
It is not a question of external vs. internal, at least not if you
consider more than SATA. Power management is the genuine task of
transport layers (specifically, of transport management layers). These
layers might need assistence from SCSI high-level protocol layer though.
IOW it's certainly correct to provide suspend/resume helpers in SCSI
high level (probably abstracted through SCSI core), but whether these
helpers are called or not has to be decided down in the SCSI low level,
or even further beneath that level.
--
Stefan Richter
-=====-=-=-= =--= ===-=
http://arcgraph.de/sr/
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