[jeff k]

I made a 160gb partition for a backup clone OS, on my 1TB Mac HD. But it's too small. Will all the new El Capitan errors with Apple mail, I
would prefer that being 300 GB. Is there any easy way to rectify? Thanks.

[reader50]

Need more info. What are all the partitions on the HD, as Disk Utility lists them? Are you booting from any of them?

Disk Utility was able to do at least some partition adjustments without losing data. But the El Cap Disk Utility has slipped a long way back. I wouldn't trust it unless someone has tried it successfully first.

I use iPartition myself, while booted from a different drive. Partitions adjusted without data loss. But it costs $50, and you need a 2nd bootable drive.

[jeff k]

Thanks Reader, you just gave me an idea.

All the Mac HD, is, is the main System on one partition of about 800 GB. The 2nd partition is 200GB, and just a clone of the OS, both bottable. I could just get another. Clone the Mac HD, test it's ok and boots ok; Wipe the Mac HD, then re partition and clone back. Right?

To think of it; using any external hardrive, and a cloning software, anyone can do anything right? Just clone to an external, wipe, re partition and clone back, am I correct?

[reader50]

True, though slow.

The old Disk Utility could adjust a partition size, so long as the beginning of the partition didn't move. Assuming your Mac HD is the 1st partition (and you're backed up), you could delete the 2nd partition. Adjust the size of the first one. Re-create the 2nd partition to desired size, then clone as needed. But I'm not sure if the El Cap Disk Utility can still do this safely.

What you've outlined is slower. But definitely safe.

[jeff k]

Actually it's all on my 3TB external -- mixed it up sorry. If I erase the small partition from a large external -150gb worth, could that new space, be absorbed into the rest of the 3TB drive?