Actually, That's a function of the ESH (6 shelves * 14 drives = 84 disks per loop).

What I'm referring to is a bit different: as you ramp up the number of drives, the performance curve begins to increase - however, after you reach a certain number of drives, the sheer work behind laying the data out on them all (and retrieving it) begins to take it's toll and flatten the performance curve. (I would assume that contention on the loop would have something to do with this as well, not that it's saturated necessarily, but that there is a bit more latency as the disks take turns passing data).

Glenn

-----Original Message----- From: Suresh Rajagopalan [mailto:SRajagopalan@williamoneil.com] Sent: Thursday, October 05, 2006 1:32 PM To: Glenn Walker Cc: toasters@mathworks.com Subject: RE: Estimating Aggregate IOPS

I see max drives per FC loop to be 84 on all filer models. Is this the limit you are alluding to?

Thanks Suresh

-----Original Message----- From: Glenn Walker [mailto:ggwalker@mindspring.com] Sent: Wednesday, October 04, 2006 3:57 PM To: Suresh Rajagopalan Cc: toasters@mathworks.com Subject: RE: Estimating Aggregate IOPS

There is a ceiling in performance gain after a certain number of disks - it's well below 112, but I'm pretty sure it's above 56 (though not much above it). At that point, the 'curve' starts to go back down again.

However, RAID-DP and RAID-4 (it's poor, homely cousin) are very fast and the filer has always handled the XORs very well for the parity calculations.

A better question\way to position this might be what type of workload\performance you expect\require. While the disks are capable of about 120 IOPS for 10k and 180 IOPS for 15K disks, the latencies begin to jump at the end of the scale - if you're workload requires lower latencies, it doesn't much matter what the disk is capable of (Exchange is a very good example of this - 80 IOPS for 10k drives is about the max you'd want to go).

Glenn

-----Original Message----- From: owner-toasters@mathworks.com [mailto:owner-toasters@mathworks.com] On Behalf Of Suresh Rajagopalan Sent: Wednesday, October 04, 2006 3:56 PM Cc: toasters@mathworks.com Subject: RE: Estimating Aggregate IOPS

Let's assume 4k IOPS. Disks are currently 10k rpm.

Are you saying that NTAP's implementation of RAID4 (or RAID-DP) gives a linear performance increase with spindles, (almost like RAID-0) and no penalty for the RAID4 or RAID-DP?

That is, aggregate IOPS is pretty much (N * disk-iops) and no penalty for RAID4 or RAID-DP?

Thanks Suresh

-----Original Message----- From: Blake Golliher [mailto:thelastman@gmail.com] Sent: Wednesday, October 04, 2006 12:41 PM To: Suresh Rajagopalan Cc: toasters@mathworks.com Subject: Re: Estimating Aggregate IOPS

How fast are the spindles, and what size is your iop? Generally, you can assume 110 per 10k RPM disk, and 180 for 15k RPM disk. This is also assuming a 10ms latency for each iop. And subtract 2 disks per raid group for raid dp (if doing writes, don't if you are doing pure reads). So with around 50 disks (after you subtract the raid dp overhead) you can expect around 5500 iops from that set of disks (assuming 10k rpm disks). For the 112 aggregate, you an expect 98 spindles and 10780 iops. I'm assuming 4k iops, and 10ms latency.

Hope that helps, -Blake

On 10/4/06, Suresh Rajagopalan SRajagopalan@williamoneil.com wrote:

Given a disk IOPS of 100, I'd like to estimate total aggregate IOPS

for

the following cases:

1. 56 disks, 1 aggregate, RAID-DP size 16
2. 112 disks, 1 aggregate, RAID-DP size 16

I'm only interested in the total raw disk IOPS available in each case, not including considering the filer head. For example, we know

that

RAID-0 with 56 disks @100 would yield 5600 IOPS.

I don't know how to do this calculation with Data ONTAP's

implementation

of RAID4 or RAID-DP.

Any assistance would help.

Thanks Suresh