Homebrew fusion drives

[smirk]

A few years back, I took apart my 2011 iMac Core i7, added an SSD, and created a homebrew fusion drive with the existing 2 TB mechanical drive. It was like getting a new computer; boot times went from 45+ seconds to something like 15 seconds, and apps felt as if they launched almost instantly.

I've been thinking of doing the same thing with my Mac Pro 5,1. The main reason is that I don't like dealing with managing and backing up two separate volumes, and repeatedly explaining to family members where they should store their data.

However, it seems that folks on here have a dim view of fusion drives. "It's two points of failure" is said a lot. Well, I suppose it is, but isn't that why we have backups?

Besides the two points of failure, are there any issues to be aware of when creating a fusion drive on a Mac Pro? Does SATA II bottleneck anything? Are there any APFS concerns?

Thanks!

 

[JedNZ]

I have a Samsung 960 EVO NMVe 500GB M.2 blade paired with a 2TB Western Digital Black Caviar HDD in my Fusion Drive - this is used exclusively for my User data. My boot drive is a Samsung 850 EVO 500GB sitting in an Accelsior S SATA III PCIe adapter.

My backups (using CCC) are fairly simple - for my boot drive it's just a 1TB spinner, and a 3TB spinner for my User data. Plus I have a 3TB Time Machine spinner for everything (all my macOS and User data), and two separate other USB 3.0 external drives, and a NAS drive. So that's my set up.

My Fusion Drive (FD) is impressively fast for saving/reading data files (R/W ~1500MB/s) because it is separate from my boot drive (R/W 525 MB/s), so my applications and macOS aren't inhibited by the User data being read/writes. I love those FD bursts upwards of 1500 MB/s when loading games, particularly the intro video components, rending video, saving graphics files etc.

Problems? I have had almost no issues with my FD in the nearly two years I've had it. I had to rebuild it once when I had weird behaviour, probably corrupted when I fried one of my CPUs. My backups saved much time and hassle restoring everything.

SATA II issues? Not any perceptible issues. SATA II is slow, and the only "slow" experience is when the FD offloads seldom used data from the NVMe to the HDD. And benchmark speed testing doesn't give me great results because one of the characteristics of a FD is that it only leaves about 4GB of room on the NVMe for new data, so when testing the speed it fills that 4GB first, and then slows continues the rest of the benchmark writing to the SATA II HDD at up to 180 MB/s. A much larger NVMe (1TB or larger) will mean more FD data is on the NVMe which will lessen the frequency of shifting often/seldom used data between the NVMe and the HDD, making for a better and faster experience.

My next purchases will be a 1TB NVMe and a 4TB WD Black Caviar to see me out for all my data requirements for the next couple of years, hopefully outlasting my cMP before I pickup a secondhand mMP (by then).

 

[tsialex]

The problem is serious and subtle, most people can't even understand it.

Apple used SLC NAND cells to make Fusion drives. SLC drives have extended longevity and usually do not have problems with repeatedly writes into the SSD space reserved for the write buffer for the HDD.

When you use a MLC, TLC, QLC, the write endurance is drastically reduced at every generation, to the point that some new QLC drives has less than 6k writes endurance, Intel 660P is one of those.

So, if you use a TLC like Samsung EVO, the Fusion Drive, more specifically the part of the SSD reserved as a write buffer prior to writing to the HDD, will fail rapidly. Every non SLC/MLC SSD drive that I used for a Fusion Drive, has reallocated sectors after some time, most failed after two years.

If you are going to do it, use a SLC/MLC drive like 970PRO, not a TLC like 970EVO.

 

[smirk]

That is really good information, thank you.

I just looked up the 970 PRO (https://www.samsung.com/semiconductor/minisite/ssd/product/consumer/970pro/) and it says it is MLC, actually.

Comparing the spec sheets of the 970 PRO and 970 EVO, it says that the PRO is warrantied for Total Bytes Written of 600TB, but the EVO is warrantied for 300TB (at the ~500GB model).

I don't know how to interpret that, exactly, because I don't know how much data Apple shuffles back and forth between spinner and SSD in typical use. If everything you write to a fusion drive first lands on the SSD and then gets moved to the spinner, then yeah... we're in trouble. But if data goes to the spinner first and then moves to the SSD only if frequently accessed, then maybe we're ok?

I know next to nothing about SSD tech, so of course I'm Googling around to read up on this stuff. According to the study reported in this article, MLCs surprisingly were found to be no less reliable than SLCs in actual use. Age, rather than usage, affects reliability, it said. To be fair, though, the usage in that study may not have included being part of a fusion drive.

 

[tsialex]

That is really good information, thank you.

I just looked up the 970 PRO (https://www.samsung.com/semiconductor/minisite/ssd/product/consumer/970pro/) and it says it is MLC, actually.

Comparing the spec sheets of the 970 PRO and 970 EVO, it says that the PRO is warrantied for Total Bytes Written of 600TB, but the EVO is warrantied for 300TB (at the ~500GB model).

I don't know how to interpret that, exactly, because I don't know how much data Apple shuffles back and forth between spinner and SSD in typical use. If everything you write to a fusion drive first lands on the SSD and then gets moved to the spinner, then yeah... we're in trouble. But if data goes to the spinner first and then moves to the SSD only if frequently accessed, then maybe we're ok?

I know next to nothing about SSD tech, so of course I'm Googling around to read up on this stuff. According to the study reported in this article, MLCs surprisingly were found to be no less reliable than SLCs in actual use. Age, rather than usage, affects reliability, it said. To be fair, though, the usage in that study may not have included being part of a fusion drive.

Sorry for the mixup with 970PRO.

The cell technology with best write endurance to the worst:

SLC, MLC, TLC, QLC. QLC has other names, depending of the manufacturer.

With a Fusion drive, the write buffer is located into the SSD. When you write anything, the OS first write it to the write buffer located into the SSD, then move it to HDD if needed, or to the other part of the SSD. So, with a TLC/QLC, you are getting into trouble fast if you use a Fusion Drive.

Another thing, Fusion drives tend to have the write buffer at the same cells, if the SSD controller don't actively move it around into the SSD, the write amplification happens fast. Apple revised the firmware of the SSD into Fusion drives numerous times, even with SLC people got into trouble with the first revisions of Fusion Drives, the first iMac with Fusion is notorious with problems.

 

[smirk]

Well, that is unfortunate. Thank you for the explanation, though!

 

[RxJemm]

The problem is serious and subtle, most people can't even understand it.

Apple used SLC NAND cells to make Fusion drives. SLC drives have extended longevity and usually do not have problems with repeatedly writes into the SSD space reserved for the write buffer for the HDD.

When you use a MLC, TLC, QLC, the write endurance is drastically reduced at every generation, to the point that some new QLC drives has less than 6k writes endurance, Intel 660P is one of those.

So, if you use a TLC like Samsung EVO, the Fusion Drive, more specifically the part of the SSD reserved as a write buffer prior to writing to the HDD, will fail rapidly. Every non SLC/MLC SSD drive that I used for a Fusion Drive, has reallocated sectors after some time, most failed after two years.

If you are going to do it, use a SLC/MLC drive like 970PRO, not a TLC like 970EVO.

Thanks Alex for this info, I used my Mac Pro 2013's SSUAX drive in my wife's iMac to create a fusion drive. Are these SLC?

 

[tsialex]

Thanks Alex for this info, I used my Mac Pro 2013's SSUAX drive in my wife's iMac to create a fusion drive. Are these SLC?

If I remember correctly, it’s made of Samsung MLC NAND. I tried to find the exact specs, only found for XP941, the Samsung OEM version of SSUAX.

 

[wulai]

If I remember correctly, it’s made of Samsung MLC NAND. I tried to find the exact specs, only found for XP941, the Samsung OEM version of SSUAX.

View attachment 807760

I used iMac 2017 ssd and 1T HDD in my Mac Pro 2012 to create a fusion drive. Are these SLC?


[doublepost=1543674520][/doublepost]Is the data secure?

 

[tsialex]

I used iMac 2017 ssd and 1T HDD in my Mac Pro 2012 to create a fusion drive. Are these SLC?

View attachment 807781
[doublepost=1543674520][/doublepost]Is the data secure?

You have to found what is the model of the blade than search what is the cell type used. Apple original SSDs made by Samsung are usually MLC.

 

[RxJemm]

Thanks TsiAlex, you are an asset to this forum!

 

[wulai]

You have to found what is the model of the blade than search what is the cell type used. Apple original SSDs made by Samsung are usually MLC.

Is homebrew fusion drives data secure?

 

[tsialex]

Is homebrew fusion drives data secure?

Depends on a lot of things. Even Apple made ones are more susceptible to problems than using the drives separated.

I stopped using Fusion drives after all the damage I found.

 

[wulai]

Depends on a lot of things. Even Apple made ones are more susceptible to problems than using the drives separated.

I stopped using Fusion drives after all the damage I found.

Thanks TsiAlex