Selecting a SSD for Fusion Drive

fusion-driveperformancessd

My aging Early 2009 Macbook White is getting a bit long in the tooth, so after learning about Fusion Drive, I'm considering combining the existing 500GB HDD with a budget-to-medium-class SSD drive, to prolong the life of the machine.

As far as I understand, Fusion Drive will fill up the drive to within 4-5 GB of its capacity.

In other news I read that some mainstream SSD controllers (eg. Sandforce) have very poor write performance when the disk is used to its full capacity.

So my questions are:

Is the "fullness" of a Fusion Drive SSD considered "full capacity" in the context of controller performance degradation?

Which aftermarket SSDs are supposed to perform consistently fast in the Fusion Drive scenario? So far I have looked at Samsung 840, OCZ Vertex 2, Agility 3, Intel 330, based on a combination of price, brand reputation and reviews – but several of them are Sandforce drives.

Thirdly, does it make sense to create an empty 8-10 GB partition on the SSD before creating the Fusion Drive, to keep the drive from filling up? And is it even possible to create a Fusion Drive on a partitioned SSD?

Cheers!

Best Answer

It is pretty close to "full capacity" (the first 117 of 128 GB are filled), but SSDs do overprovisioning for this reason.
As long as you have enabled TRIM on your SSD, you should be fine. I keep my (non-Fusioned Crucial RealSSD 300) SSD near full capacity and don't experience degradation, as long as I have TRIM turned on (if it's turned off it gets terrible fast).
Yes, you can create a Fusion Drive by specifying the partitions, e.g.:

diskutil cs create fusion /dev/disk0s2 /dev/disk1s2

If you are looking for non-Sandforce controlled devices, you have many options now: Crucials M4/M500, Samsung SSDs, OCZ Agility/Vertex 4, and more.

For further reading, check out AnandTech's article with more details and pretty graphs.

Related Solutions

Fusion Drive: free space on SSD

At least 4 GB of the SSD portion of a Fusion drive is left empty at all times. That space is used for incoming writes. If there's less than 4 GB of empty space on the SSD, Core Storage will start offloading data to the HDD.

So if all your data is less than your SSD capacity less 4 GB, then you have whatever your SSD capacity is (128 GB on all Apple supplied Fusion drives) minus the amount of your data. Otherwise, you've got 4 GB free.

As an aside, the reason df doesn't work in this case is that it only reads filesystems. The filesystem sits atop the logical volume created by Core Storage (the software behind Fusion) — there's no "SSD portion" or "HDD portion", to the filesystem it's all one big drive.

MacOS – Fusion Drive, Bootcamp and FileVault – with working Recovery HD

OS X Internet Recovery
Mac models introduced after public availability of OS X Lion include the ability to start up directly from an Internet-based version of the OS X Recovery system. OS X automatically uses this feature when the Recovery System on the hard disk isn't available (such as when your hard disk encounters an issue, or when your hard disk has been replaced or erased).

My setup is a Mac mini 2011 with a DIY Fusion drive (840 Pro + 1 TB Hitachi). The Fusion drive was built on 10.8 and then the machine was upgraded to 10.9.

diskutil list 
/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *256.1 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:          Apple_CoreStorage                         255.7 GB   disk0s2
   3:                 Apple_Boot Boot OS X               134.2 MB   disk0s3
/dev/disk1
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk1
   1:                        EFI EFI                     209.7 MB   disk1s1
   2:          Apple_CoreStorage                         934.5 GB   disk1s2
   3:                 Apple_Boot Boot OS X               650.0 MB   disk1s3
   4:       Microsoft Basic Data BOOTCAMP                64.9 GB    disk1s4
/dev/disk2
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Fusion HD              *1.2 TB     disk2

When I press alt, I get three entries, Fusion, Fusion, Boot Camp. Either Fusion being selected boots the main OS. Bootcamp boots Windows.
⌘R boots local Recovery HD (not Internet Recovery). I have a choice of Wi-Fi, if I need Internet Recovery.

In your case, is it possible the Recovery HD is damaged?

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