# Hybrid Drives (SSHD)



## GROND (Feb 12, 2014)

Has anyone used one of these hybrid drives (SSHD) that has a built-in NAND flash storage? I was looking at the Seagate ST2000DX001 for a desktop or a Seagate ST2000DX001 for my laptop. They have standard magnetic disk storage (1 or 2 TB) with a built-in 8GB flash. How do these perform under ZFS, and what kind of configuration does it involve? Is the drive presented to the OS as a single disk (the disk does the caching itself) or does the OS see the disk and the flash as two separate devices (manually configure ZFS to use the flash as cache)? Are these reliable? Any thoughts would be appreciated.

*EDIT: Just realized those Seagate product numbers are the same. One is the 3.5"/2TB model, the other is the 2.5"/1TB.


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## wblock@ (Feb 12, 2014)

The flash memory is supposed to be transparent to the computer.  All it sees is that common requests are much faster because they come from flash instead of off the drive.

I have not tried any of the hybrids.  It would be interesting to see a benchmark comparing ZFS on one to ZFS handling a separate SSD.  However, they are probably pretty difficult to benchmark.  The internal firmware tracks the most frequently-read blocks and keeps them in flash.  Many benchmarks would make that invisible, and some would overemphasize it.


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## phoenix (Feb 13, 2014)

It depends on the drive.

Some of the hybrid drives show up as two separate drives and require special configuration and drivers to be used as a single volume.  I believe the Western Digital drives are like this.

Others show up as a single drive and the firmware on the drive handles everything internally, moving or copying data to/from the SSD side of things.  I believe the Seagate drives are like this, although I vaguely recall some of their earlier attempts required a special Windows driver.

You definitely have to read all the fine print to see how things work for each specific drive.  It's really a mess right now.


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## GROND (Feb 13, 2014)

If they're risky, then I'll just go for something else.


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## throAU (Feb 14, 2014)

I've run a Momentus XT 750 in my MacBook Pro for a year.

I like.

I don't think I'd buy a regular hard drive again, if there was a hybrid in the size I was looking for.

It's not completely SSD fast, but it boots quick (cold boot in 12-13 seconds from power button press, including the OS X EFI post) and is definitely quicker than a regular disk.

I've had zero problems in just over 12 months now.  And yes, to the OS, they just look like a regular disk - the cache is totally transparent.  While I was installing some software a while back, I was seeing 18,000 (? it was a while, ago, I think that is correct) IOPs on it at one point.  There's no way a spinning disk will do anything like that, even temporarily.


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## jalla (Feb 14, 2014)

I've used a hybrid Seagate 500Gb for 15 months in a Dell laptop. It looks and behaves like any regular drive and the inner working is completely hidden and independant of the operating system.

Generally I'm happy with it, but on rare occations the disk seems to be actually "thrashing". I.e. with a lot of concurrent IO I've seen the machine freeze for 10-20 seconds with the hdd activity light constantly on. It's so rare that it doesn't bother me though.


```
ada0: <ST500LX003-1AC15G DEM3> ATA-8 SATA 3.x device
ada0: Serial Number W200646L
ada0: 600.000MB/s transfers (SATA 3.x, UDMA6, PIO 8192bytes)
ada0: Command Queueing enabled
ada0: 476940MB (976773168 512 byte sectors: 16H 63S/T 16383C)
```


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