Cluster / allocation unit size for 1 TB exFAT backup drive?

[Eug]

The default 262144 byte cluster size Windows 10 chose seems way too big. For 40.1 GB worth of files, it took up 44.2 GB. That means an extra 10% space was wasted.

I copied over these backup directories to my NTFS boot drive with a cluster size of 4096 bytes, and 40.1 GB took up 40.1 GB. ie. The actual data vs data on drive usage were almost the same.

So, I am going to reformat this hard drive. What would you recommend for exFAT? Perhaps 16 KB? I'm thinking 4 KB might slow down the drive somewhat. The files are a mix of small files, eg. 5-100 kb, up to larger files of a few MB. Files larger than 100 MB would be uncommon.

BTW, this is a USB 2.5" platter drive.

 

[Eug]

Hmm... I found this comparison, on a 2 TB 3.5" drive:

https://ejrh.wordpress.com/2012/10/26/cluster-size-experiment/

It seems for large files, the sweet spot for speed was between 4 KB and 64 KB, with 8-32 KB probably best.

For small files 4 KB did really well but 64 KB was better, and 32 KB was noticeably worse, so that's much harder to understand.

I think I might give 16 KB a try.

 

[Eug]

Arrrggh! I formatted it as mentioned above, and started a file transfer.

I was wondering why my file transfer was taking so long and then noticed my free space was dropping like a rock. I was about half way through a 30 GB transfer and I had already used up 190 GB. WTF?!?!

It turns out Windows 10 doesn't allow you to format a 1 TB exFAT drive with a 16 KB cluster size. The minimum is 64 KB. I had chosen a size of 16384, but it was 16384 KB, which is 16 MB. (!) Oops.

So, I guess I'll just have to stick with 64 KB. I wonder if I'll be able to do 16 KB on Win 7, but I don't have a Win 7 system handy right now.

 

[grimpr]

Just go with defaults on ExFAT and 64k on NTFS.