RE: Mirroring, Striping, Etc.

Mitchell B. Wagers ( (no email) )
Wed, 04 Feb 1998 16:05:14 -0800

A single drive can't come close to 40mb/sec, only system I've seen that
comes close or beyond that across multiple drives is Sun's Enterprise
Array, but that still isn't host-to-drive speed. If you are maxing the
transfer speed of your drives out while on a single channel, you have two
things to look at. The 2940 does 40mb/sec, total BURST rate. I should have
stuck in there that it isn't the two channels that makes the difference,
it's that both channels operate off a separate processor on the card
(3940). You can put two UW SCSI 3 drives on one channel and be limited by
the cards burst rate, because the drives can burst well over 20mb/sec,
totalling well over 40mb/sec that's handled by the card. See my point now?
Maybe I was pointing more towards planning for the future...but it was just

In my view, servers that sustain, for a long period of time, maximum
throughput on any given piece of hardware are going to die well before
their time. Drive a Geo Metro at 111mph for 365 days, it probably won't
last very long.

At 01:26 PM 2/4/98 -0800, you wrote:
>Actually, the 2940 can take several drives on it's single channel before
>there would be ANY advantage of a 3940. Reason being, the SCSI bus is
>something liek 80mb/sec, whereas a single drive can't come close to that.
>You only need consider another channel if you can do the math of adding up
>the peak of your drives and seeing if it adds up to more than the channel.
>At 02:26 AM 2/3/98 -0800, you wrote:
>>Mirroring is usually slower unless the SCSI card can do it for you, not the
>>case on most Adaptecs. Stripe the set, although you will lose the "mirror"
>>type backup of mirroring, but it will increase performance. Also, the 2940
>>is a single channel SCSI host, going up to a 3940 and putting each drive on
>>separate channels would probably help, but you would need to find out what
>>kind of internal bandwidth the hard drives are using on your SCSI
>>card...hmmm...I'm not sure how to make this much clearer. :) Going to a
>>3940UW would mean upgrading to UltraSCSI 3 WIDE.
>>From: Gregory White
>>Sent: Monday, February 02, 1998 2:27 PM
>>Subject: Mirroring, Striping, Etc.
>>Can someone offer some information regarding performance
>>improvements/degradation caused by drive mirroring and striping on NT 4?
>>We recently added a second drive to our mail server and set it up as a
>>mirror drive. Since then, it seems to be slower in responding when sending
>>mail. It may just be perception, since I am paying more attention to the
>>machine now.
>>We are running a PP150 w/128 MB Ram and 2- 2.1 GB SCSI on an Adaptec 2940.
>>Thank you,
>>Greg White
>>Direct NET Communications
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