Date: Mon, 13 Dec 1999 11:07:21 +0100 From: "Oliver Blasnik" <ob@omnilink.net> To: <freebsd-scsi@FreeBSD.ORG>, "Mike Smith" <msmith@FreeBSD.ORG> Subject: Re: Again: CRD-Raid-Controller and FreeBSD 3.x Message-ID: <000c01bf4551$d8862240$da1940c2@omnilink.de> References: <199912130832.AAA06120@mass.cdrom.com>
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Mike Smith wrote:
> No. FreeBSD starts assuming that a drive will handle 64 tags, but it=20
> expects that the drive will correctly report a queue-full condition so =
> that it can dynamically adjust this number downwards.
And this could not work as far these maximum of 32 commands is =
host-based, not lun-based.
=20
> If the problem in this case is that the CMD unit is accepting a tagged =
> command and then simply throwing it away, that's a bug in the CMD=20
> firmware.
Correct.
=20
> This may solve the "problem", but it will substantially degrade=20
> performance in the case where there's only one array on the =
controller.
Right. But on the other hand enables tq without bothering on =
system-crashed :)
Better slow than not running.
=20
> <shameless plug>
> You might want to consider using a PCI:SCSI RAID controller like a =
Mylex=20
> DAC960 or AMI MegaRAID. The host:cache bandwidth is _much_ better on=20
> these units, and they typically offer all of the features of the =
external=20
> units at a lower price.
> </shameless plug>
*g* Not a possibility for me.
It has to be external for different reasons. We do not only have =
FreeBSD, there's also Solaris and WinNT. Connecting an external system =
enables transparency. Some CRD's are connected to two machines, =
sometimes to share the array, sometimes to enable high-availability for =
a system (hot-take-over of the drives). You could set up two CRD's to =
the same drive bay to enable renundancy and cut off this single point of =
failure. Last but not least, if one machine burns down, just take a new =
hardware, plug it onto the raid and switch it on - running and up again. =
Tell me how to do that with your controllers :)
Cu, Oliver
PS: I made a mistake on my cam_xpt.c-entry. the "min-tags" has to be >0 =
to enable tq :)
--=20
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