Cisco 3750G flash/nvram free space and filesystem geometry

I'm trying to copy a file to a 3750G's nvram: that is smaller in bytes than the filesystem's listed free space in bytes. However, the transfer aborts with:
%Error writing nvram:blah (No space left on device)
I assume this is because the free space does not indicate unallocated free space, just filesystem capacity minus straight used space (so if it's a 524288 byte filesystem with 2k blocks, and I have two 100-byte files, it would show 524088 bytes free but I couldn't actually put anything larger than 520192 bytes).
Is there a way to find more details on the flash/nvram filesystems in these switches? Either through Cisco documentation or a CLI command to show filesystem geometry? Something that could show me actual usable space would be fantastic.
FYI right now the nvram: filesystem has two files of 0 bytes, is showing a capacity of 524288 bytes, with 524236 bytes free.