Compqay Storage Array Performance

Hi All,

I am currently using "Compaq RAID Array 4100" as the storage server.

Under the following two links,

I foudn the max. bandwidth for FC-AL switch is 500MB/s
and the max. transfer rate for PCI Model 64-bit/66-MHz host adapter is 100MB/s

By these two figures, can I draw a conclusion that the max. throughput to my raid array is 100MB/s only. The bottleneck is at the PCI host adapter.

Please correct me if I am wrong.

Who is Participating?
>I foudn the max. bandwidth for FC-AL switch is 500MB/s

No, it's 1000 Mb/s which once protocol overhead is taken into consideration is 100MB same as your card. the 500MB/s you've found is probably the backplane speed - i.e. the max bandwidth available to all ports on the switch so if it has 8 ports you get 500/8 MB/s per port assuming all ports are in use.

The bottleneck is almost certainly the disks.
cplauAuthor Commented:
Dear andyalder,

I'm not sure how many PCI host adapter has been installed.

one card is serving for one port? true or false?

If only one PCI host adapter is installed, how can it handle the total transfer rate for 500MB/s

Please advise.
As Andy states above, the calculations rarely match up that easily.

FC-AL switches are on the 500MB/s backplane. On a 8 port switch this would equate to approx. 62MB/s per port, assuming all ports in full use.
The HBA working on 66Mhz and 64-bit would work happily at 100MB/s per port.
The disks would sit within a chassis that is running a backplane speed of approx 3.2GB/s (1.6GB/s looped)
The Compaq 4100 storage array has 12 drives therefore they can be fed by 273MB/s speeds (136MB looped)
The drives themselves run at 10KRPM with a transfer rate of 256MB/s max speed.

Therefore, if you have a single server, with a single HBA connection you will not be able to drive the spindles at max transfer rate as the PCI bus will be a weak point (assuming your server is not restricted in any other way).

However, if the SAN is fully populated with 8 servers, then the bottleneck becomes the switch in this scenario. Change the switch for a E16 Fabric swicth and the bottle neck will move once again to the disk spindles. Upgrade these, and the backplane becomes the bottleneck.

There will always be a bottleneck, you just need to know what you are actually expecting to drive it with. In most cases (average transactions and performance) you would expect the switch to be the bottleneck, or the drive performance.

Hope this helps
The controller in the RA4100 is max 100MB/s so there's no way of speeding it up unless you move the disks to a faster box like the MSA1500cs, and then you would be using Ultra 3 disks in a U320 backplane, the quickspecs are at

Even with a redundant controller I'm pretty sure it's active/passive so 100MB/s is the top speed you'll get.
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