A lot of it depends on the kind of device you are procuring, its configuration and setup. If you have fair mix of SSD and spinning devices, then you should be good. While designing the storage, account for the latency as well - Isilon doesn't work so well with high latency environments.
For the vaults, we did some tests last year and the RT for file upload for the end users between a NAS and a DAS was not significantly different. But when we had to do a data migration (a big bang), it really impacted our timeline. When you have a loader running for a long time, writing a bunch of data, IOPS tend to go down over the time.
Performance impact with large number of files, to me it sounds like a problem with the configuration/setup - inodes mirrors + cluster + drive configuration is where you can look at to find the root cause of this. You can control the number of files Windchill should write to a folder as well. Also if you have a multiple vault configuration, you can have the default upload on a faster drive too.
I am a big fan of snapmirror with NetApp. it really helps in data refresh, DR and so on.
Thank you
Binesh Kumar
