Date: Wed, 11 Nov 1998 08:46:03 +1100 From: Peter Jeremy <peter.jeremy@auss2.alcatel.com.au> To: hackers@FreeBSD.ORG Subject: SCSI tagged queueing and softupdates Message-ID: <98Nov11.084659est.40344@border.alcanet.com.au>
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AFAIK, SCSI tagged queueing is the default in 3.0 (via cam or inside the ahc driver). (This was optionally enabled via AHC_TAGENABLE in 2.x and the 3.0 man page still describes this option, although the option is gone). According to the description, tagged queueing allows a SCSI device to re-order pending I/O requests in order to improve throughput. Soft updates, on the other hand, rely on the correct sequencing of physical writes to ensure that the disk metadata is consistent. Is this a real issue? If so, it would seem that tagged queueing must be disabled (at least for writes) when softupdates are enabled. It's not obvious to me that this is currently done (or even easy to do). Comments please. Peter -- Peter Jeremy (VK2PJ) peter.jeremy@alcatel.com.au Alcatel Australia Limited 41 Mandible St Phone: +61 2 9690 5019 ALEXANDRIA NSW 2015 Fax: +61 2 9690 5247 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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