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My second hard drive (WD 640 megs) has a cluster size of 512 bytes. I want to change it to 4kb. I tried doing it with Acronis Disk Director 10 and when it boots to try to do it, I get this error:

Operation error: Internal error: empty destination block

So how the hell do I change cluster size?

I seem to remember that cluster size is determined by the OS. Why change it? you may have just made the disl unusable by windows, hence the error message.

While I'm sure there are utilities that can change it on the fly, I personally wouldn't change it without backing up the partition, deleting it, and repartitioning with the new cluster size. Partition Magic will do this.

However, I see no reason to change the default cluster size. With the size of the cache on modern hard drives, there's no real performance benefit. IMO

Well 512 bytes is not the default cluster size for a over 500 gig hard drive. 4kb is the default. Here are some defaults

Drive size
(logical volume) Cluster size
----------------------------------------------------------
512 MB or less 512 bytes
513 MB - 1,024 MB (1 GB) 1,024 bytes (1 KB)
1,025 MB - 2,048 MB (2 GB) 2,048 bytes (2 KB)
2,049 MB and larger 4,096 bytes (4 KB)


I have copied over the files on my hard drives many times as I was upgrading in hard drive size. I think way back on a smaller drive, it was 512 byte clusters and when copying to new hard drives, this got carried over and I never knew it until recently.

The way I found out actually was when I bought PerfectDisk 10 and couldn't do an offline defrag. The PerfectDisk tech support was having me do all kinds of tests and they came up with this conclusion. Here is their quote.

You seem to be running out of memory. For your version of Windows the maximum non-paged pool, which is the type of memory that PD uses at boot time, that Windows allocates is 256MB. Windows will take what it needs to load first and then leaves the rest free but what's left is not enough for PerfectDisk to run.

The issue is that you have a 500 GB drive with a 512byte cluster size. There is not enough memory on your system to support this cluster size. Under certain circumstances, PerfectDisk will be able to defragment a drive with 512 bytes but the log shows insufficient system resources exist to complete the requested service. You have a very large drive formatted with 512 byte clusters. With this cluster size it is taking about 8 times as much memory as 4k clusters would. If you convert to 4k clusters, this won't be an issue.

That's when I started trying to figure out how to change it. Disk Director 10 just cannot do it. I then installed Partition Magic 8 and tried again. Partitiion Magic 8 had no problems at all doing it, although the process takes quite some time to complete, around 1-2 hours per hard drive. I finally got it done with no loss of data whatsoever and now PerfectDisk 10 runs the offline defrags just fine.

I got my little lesson on cluster sizes, something of which I had never paid any attention or even knew anything about it really. There are discussions throughout the net (though most of which are quite dated) of supposed performance benefits from changing to larger cluster sizes on big hard drives (cluster sizes can be changed all the way up to 64kb) but I just stuck to 4kb. This 4kb default was set way back before hard drives ever got to the capacity they are now. I'd like to see that number revisited out of curiousity to see if higher than 4kb is really beneficial for the larger drives of today.

Cool. I didn't know Partition Magic would even do it on the fly.

It does have to reboot and then does it before Windows, the same way PerfectDisk does the offline defrag. Both Disk Director 10 and Partition Magic 8 have the option to do this but only Partition Magic 8 can actually do it. I emailed Acronis about this issue, I hope they will fix it.