Slashdot Mirror
Hybrid Storage Solutions Compared
Vigile writes "While few would argue with the performance advantages of solid state drives, the relative cost compared to spindle-based disks still make them a luxury item. The promise of hybrid storage solutions is to combine the benefits of both — large capacities with standard drive technology and performance advantages of solid state. PC Perspective published an article comparing several different solutions that vary in their approach to hybrid storage. The OCZ RevoDrive Hybrid combines a standard 2.5-in drive with a PCI Express-based SSD that offers the best overall performance and largest cache size. Seagate's new Momentus XT 2.5-in solution embeds the cache on the PCB of the drive, allowing notebook users to install this solution easily. Finally, the Intel chipset-based caching option combines either a 2.5-in or mSATA SSD with a standard hard drive on either desktop or mobile platforms, allowing the most flexibility of any other hybrid solution. All three have advantages for specific consumers, though, and varying performance levels to go along with them."
The limit of an ssd's max writes is high enough that time wise a mechanical hard drive is more likely to fail during the normal lifespan.
Facebook released, some time ago, their Flashcache solution. It works similar to ReadyBoost, et al, except it works on Linux, and "pairs" an SSD with a hard drive. Very useful.
http://www.facebook.com/note.php?note_id=388112370932
Seagate's new Momentus XT 2.5-in solution
Had a 500 GB version in my laptop since they came out last year (Summer I think) And yes, it's much faster than a typical 7200 rpm drive.
The best thing about a boolean is even if you are wrong, you are only off by a bit.
According to Seagate the Momentus XT will fail back to being a regular hard drive if flash failure is detected by the controller. All data in flash is also stored on the drive, the SSD part only caches a copy of already stored data for faster read performance.
EA David Gardner -"... but the consumers have proven that actually what they want is fun."
What I want is a filesystem that can use a partition of an SSD and a partition of a rotating magnetic disk. Metadata, directories and small files on the SSD, big files on the rotating disk.
This ought to be fairly simple - anyone fancy hacking ext4?
According to Seagate the Momentus XT will fail back to being a regular hard drive if flash failure is detected by the controller. All data in flash is also stored on the drive, the SSD part only caches a copy of already stored data for faster read performance.
That's obviously true for reads, but is it true for writes?
These hybrid devices typically have a battery (excuse me, "super capacitor") to flush any cached writes out to disk.
But what if the OS thinks data was written (because it went to the SSD cache successfully), but flushing from cache to disk fails because something broke on the SSD side?
SSD controllers haven't been exactly stellar in terms of reliability so far.
For my money, I just got two 256 GB Crucial M4s, and I do daily full-image backups (excluding *.bt! and any steam games) to an external 2 TB drive.
Doesn't really matter.
Anand from Anandtech writes:
My personal desktop sees about 7GB of writes per day. That can be pretty typical for a power user and a bit high for a mainstream user but it's nothing insane. ...
If I never install another application and just go about my business, my drive has 203.4GB of space to spread out those 7GB of writes per day. That means in roughly 29 days my SSD, if it wear levels perfectly, I will have written to every single available flash block on my drive. Tack on another 7 days if the drive is smart enough to move my static data around to wear level even more properly. So we're at approximately 36 days before I exhaust one out of my ~10,000 write cycles. Multiply that out and it would take 360,000 days of using my machine for all of my NAND to wear out; once again, assuming perfect wear leveling. That's 986 years. Your NAND flash cells will actually lose their charge well before that time comes, in about 10 years.
--You will rephrase your request for me to go to hell. Goto statements are not acceptable programming constructs
Adaptec has a new technology called Hybrid RAID, which uses 50% SSD/50% HDD in RAID 1 or RAID 10. Reads are serviced by the SSD(s) only. It seems to me you might need to short-stroke the HDD in order to make this a reasonable approach.
Their new 6E series is very inexpensive for 6Gb SAS cached (128MB) hardware RAID; 6805E is (8 int. ports) is about $225 retail:
https://www.adaptec.com/en-us/products/controllers/hardware/sas/entry/sas-6805e
I'm no shill or fanboy; I just found this interesting and relevant.
Thank you, Edward Snowden.
"Arguments from authority are worthless." —Carl Sagan
You can purchase 24 GB of ram for less than $200 today. I would love to see a side by side performance and energy consumption comparison with someone who decided to spend their extra money on DRAM.
I suspect what you'll see is that after a day all read operations are resolved instantly from the OS disk cache without the performance and power hit of flash. If you have write intensive workloads the current crop of SSDs would not be for you anyway.
That article talks about enterprise drives which use SLC flash. SLC has 20 - 30 times the write endurance of the MLC flash you get in consumer-grade SSDs.
SSD controllers are good enough now that I wouldn't worry about the MLC flash in my laptop's SSD for general use, but I'd take a very close look at the numbers if I was using it to do anything that was write heavy (like video work or building a big codebase).
Chernobyl 'not a wildlife haven' - BBC News