[vdr] Is there a way to give inode entries a higher cache priority than data in the linux kernel?

I have a distributed VDR system in my house with a lot of disks that are NFS mounted by VDR PCs in two rooms. In order to conserve energy, I have used hdparm to set a spin down delay after which the disks turn themselves off. When /video/.update is touched (one of the VDR PCs creates/deletes/ edits a recording, I move a recording into a folder, etc.) or when the vdr program is started, it reads all directories from all disks. Most of these directories are unchanged, so there really is no need to spin up the disk just to read a few inode entries. However, my observation is that they are always spun up. So my questions are:

1) Is there a bug in the linux kernel that makes it spin up the disk needlessly even if the data are still in the cache?

2) Is there a way to configure the kernel, so the inode entries are locked in the cache or at least get a much higher cache priority than ordinary data?

Thanks and Cheers, Carsten.