Re: SCSI drive replacement using SD?

From: Justin <>
Date: Mon, 3 Nov 2014 18:17:59 -0500
Message-Id: <>
I think it’s important to maintain perspective on the difference between the nominal performance limits of the bus and the real world performance of the system the bus is included in.  SCSI should’ve done 5MB/s but most of those 68k macs couldn’t do that even if the drive was just a box of RAM because of the realities of their overall bus architecture, clocks, driver quality, very weak multitasking in the kernel, who knows what else, etc. This thing seems to saturate the narrowest part of the pipe on the ones people have posted numbers for.  I have a PowerMac 9600 here because it was the last machine Apple built that could read their 400k floppy format, and is therefore the easiest to get onto a modern ethernet network and talk to something else with. That will probably be the machine that I stick this thing in first.

What I have not seen is a post regarding its latency.  I would be very interested in knowing what its random read latency is across the emulated drive, particularly as a function of card size and speed rating. A lot of the posts talk about using pretty small SD cards but they only talk about class 10 or unlabeled.  I have a lot of the 32GB SanDisk Extreme Pro cards that are rated for 95MB/s so I’ll probably be using those at least at first. I’ll be interested to see how that behaves. I think that latency has much more impact on the normal user experience than pure sequential read or write speed across the bus.  It’s not as if anyone is going to use this thing in a media server of some kind.

In that 9600 I currently use two 7.2k RPM Barracuda drives in software RAID on an Adaptec 2940UW card (a PC one that I bought for nothing and flashed the PowerDomain firmware into for a tiny fraction of the price). I’m always worried that these or the drives in my Amiga are going to crap the bed, and they are really annoyingly loud to leave on all the time anyway, so I do not leave these machines hot with the drives spinning. Anyway, I’ll be very interested to see how the system “feels” in terms of boot time and latency booting from this thing. Maybe I’m officially old, I used to have a ton of fans crammed into my PC’s and they all sounded like jet engines, and now I have a Mac Pro sitting here effectively dead silent even with all cores pegged.

FWIW for those who got errors, the site told me the thing was out of stock but let me place an order anyway.

> On Nov 3, 2014, at 11:14 AM, wrote:
> On 2014-11-03 16:50, Per Olofsson wrote:
>> At half the price of a 7720U it looks like a pretty good deal, but it
>> looks like it's currently limited to about 2.5 MB/s which is a bit too
>> slow for my taste:
> That's what I was wondering - if that's the limit of the device or the Mac they tested it with. If that's the limit of the device/firmware then you are not alone in your taste.
> P.S. Maybe we should look at it this way: less than half the price = less than half the performance ;-)
> -- 
> SD!
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Received on 2014-11-04 00:00:03

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