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SubjectRe: What still uses the block layer?
On Tue, 16 Oct 2007, Matthew Wilcox wrote:

> On Tue, Oct 16, 2007 at 12:54:58PM -0700, david@lang.hm wrote:
>> On Tue, 16 Oct 2007, Alan Cox wrote:
>>> I wouldn't try dividing those by pata v sata. You'll cause all sorts of
>>> problems in the process because of PATA-SATA and SATA-PATA bridges.
>>
>> if you use a PATA-SATA bridge (IDE drive SATA controller), it would look
>> to the system like a SATA drive and be addressed and enumerated as SATA.
>
> But you don't know where the bridge is. It might be on the drive's
> board, it might be an explicit enclosure, or it might be on the
> motherboard. Each of those scenarios is going to have a different user
> expectation.

the only one of these that I would find unexpected would be the one on the
motherboard.

why is this any different from the external enclosures? they have always
appeared as the type of device that connects them to the motherboard, (and
even with SCSI, there are some controllers that don't generate sdX
devices)

the driver for the controller is what has historicly determined what the
device appears as to the system. an example of this is the 3ware driver
that is a SCSI drive but the drives attached to the card are IDE drives.
another example is the I2O drivers (which give you access to the Raid
array and to the individual drives, in different namespaces). while I may
disagree with some of the selections that have been made (the 3ware has
always seemed odd to me for example) it's pretty simple to figure out.

but in any case, historicly IDE (PATA) and SATA drives have been handled
differently, IDE drives have had fixed device names based on how they are
connected, SATA devices have had 'order found' device names from the SCSI
heritige. mixing the two types into one namespace requires changing one or
the other. while I would love to see SATA gain hardware path dependant
names I'm not holding my breath, but I hate to loose the predictable
nameing (even if the names change) for the IDE drives.

David Lang

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