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SubjectRe: XFS and journalling filesystems
Hi,

On Sat, 29 May 1999 10:44:55 -0700 (PDT), Tim Smith <tzs@tzs.net>
said:

> On Thu, 27 May 1999, Theodore Y. Ts'o wrote:
>> DMA in and out of memory, I was appropriately horrified. I'm glad to
>> hear it wasn't true, and that you had no part in implementing or
>> designing such a horrible hack (i.e., direct device-to-device I/O). :-)

> Is direct device-to-device I/O always bad?

Not exactly, but often. It complicates things like error recovery
enormously, and it rapidly becomes useless as soon as you have devices
on multiple buses (although SANs such fibrechannel fabrics do help
there). As long as you have spare bus bandwidth, doing zero-copy
transfer through the OS is as fast, and it is much cleaner.

--Stephen

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