Had to re-create my fusion drive I have questions

[dimme]

I had to re-create my fusion drive on my late 2015 iMac. I used terminal to create a new core storage unit. I am currently restoring from my Superduper backup. I am wondering what the best way to recreate the recovery partition. In the past I have used recovery portion creator but I do not think it works with fusion drives.
Also I had read that when apple creates a fusion drive there is a portion of the SSD (i think 4 GB) used as cache. Is that automatic or do I need to create it if so how.

Lastly I was very happy with the performance of the fusion drive, will the drive automatically sort it self out and put the os and other commonly used files on the SSD?

Thanks

 

[maflynn]

There's some good questions that I'm also interested in seeing answered.

As for the recovery partition, wouldn't a reinstall of the OS create one, i.e., doing an internet recovery will recreate that partition? Secondly since you can do a internet recovery, is a recovery partition needed all that much (unless you're going to FileVault which that process uses the recovery partition)

 

[dimme]

I ended up installing el captain over my Superduper backup, which gave me back my recovery disk and also seemed to fix a few little quirks. I have a 2012 mac mini with a fusion drive at work and ran AJA System test 2.1 on the mini and my iMac with my recreated fusion drive. With a 16GB test file the iMac starts out faster but about 1/4 of the way through it slows down. The read speed is very fast. The mac mini stays constant through out the entire test. I not sure what this means. So if anyone has some insights I would appreciate it

 

[dimme]

Anyone with a late 2015 5K iMac with a 2 TB fusion drive care to post a benchmark with AJA System test 2.1 showing the graph. I would appreciate it. I just want to see if the fusion drive I created is working as good as the factory setup. It feels good to me but I just want to check.
Thanks

 

[maflynn]

Here's what I have, the results seem a bit slower then yours.

I guess I can attribute the write speed difference because you ran yours off a freshly formatted computer and I have one that may be a bit more fragmented - I don't know to be sure.

As for the read speeds, I have no idea. I ran this twice and the results were about the same.

My iMac - M395 2015 iMac with 2TB Fusion drive and 8GB of ram.

 

[bogg]

I am currently restoring from my Superduper backup. I am wondering what the best way to recreate the recovery partition. In the past I have used recovery portion creator but I do not think it works with fusion drives.

The method I used might not be the easiest but I removed the fusion drive all together and when installing formatted the whole HD as my system drive, this created a Recovery Partition on the HD, I then, after the installation but without going through the "Setup your mac"-guide at first boot deleted the primary system partition on the HD, used the space created and the whole SSD to create a new fusion drive, then I reinstalled the OS on this new partition, the recovery partition on the HD is then left intact.

Also I had read that when apple creates a fusion drive there is a portion of the SSD (i think 4 GB) used as cache. Is that automatic or do I need to create it if so how.

Yes, it will automatically reserve a bit of the space (~4GB) as write cache/scratch space, this is used for the OS when it needs to speed up write operations, like when working with files (extracting them, downloading and so on), those are automatically put on the SSD and later moved to the HD if deemed less used than other blocks on the SSD-part (AFAIK).
On the 2015 iMacs with 1TB Fusion this means that out of the 24GB SSD on there, 4 is reserved straight away, another 8GB or so would be kept by the Sleepimage (depending on your RAM size ofc), this will most likely also reserve space on the SSD (otherwise Apple wouldn't recommend the current 2TB Fusion over the 1TB Fusion.
Really just leaving 12GB of space for CoreStorage to do it's fusion magic, this would explain why the 1TB Fusion of the 2015 iMacs feels so much slower than the 2TB version which sports a 128GB SSD instead, it really is ~8 times smaller when subtracting all reserved space and otherwise claimed space. Also blocks for OS X will inhabit the SSD as well, like the dock and most system files used when actually using your computer. The current 1TB/24GB Fusion drive would more or less only speed up writes (by the 4GB cache), sleeping and normal system use (due to OS X residing on the flash). There's more or less no real space for larger applications to reside on the SSD.

Might not been what you asked and chances are you don't have the 1TB/24GB (2015?) version of fusion drive.

Lastly I was very happy with the performance of the fusion drive, will the drive automatically sort it self out and put the os and other commonly used files on the SSD?

Yes