I had the same issue:
A formerly great performing Sandisk EXTREME Stick 64GB was down to 24MB/s write speed after formatting it to NTFS.
However, how weird is it that SanDisk doesn’t care to provide a Tool to help users store >4GB files
on the most common File System?
Instead we are blamed to have formatted our devices.
(Silly ideas these customers … )
Fact is that SanDisk does not provide adequate tools for aligning partitions / sectors properly.
Something that is well known to be important for drive performance.
Oh, of course that’s something SanDisk support doesn’t tell us.
I was able to fix the problem with HPUSBDisk.exe.
Remember: Don’t blame me, if something goes wrong! It’s your risk if you damage your Sandisk with that tool.
