SSD drives are fairly new, they are currently quite expensive and, they have only recently entered into the mainstream market.
Currently there are two types of SSD drives sold as complete products.
SLC (Single level cell) these are high performance and high price, they generally also have a fairly large cache (64MB) is not uncommon. Prices range from about Â£400 for a 32GB model to several thousand for higher capacities. Generally speaking, SLC based drives are aimed at the enterprise storage market, where high performance and reliability is a must.
MLC (Multi level cell) these are once again high performance, in fact, very often faster than their SLC counterparts when reading. They are aimed at the mainstream/enthusiast market. Prices start at around Â£90 for a 32GB model. MLC drives do have some shortcomings. Most of the MLC based SSD drives are generic and are built on a JMicron controller with Samsung MLC NAND flash memory. They also in most cases, have very little cache compared to their SLC counterparts. Although no one is prepared to give clear details, it is suggested the cache on MLC based SSD drives is as little as 256KB.
MLC also has latency problems when small random files have to be written to the drive. The problem can be quite noticeable because many of these small random files are written in the background by the operating system. The problem manifests itself by making the PC pause or stutter, from a fraction of a second to several seconds.
So how can we eliminate the pausing and stuttering?
This was actually quite easily solved, but at a price. A hardware RAID card with onboard cache is required. These are fairly pricey. They start at around Â£100 for a PCIe x1 card with 128MB of onboard cache and a Marvell 400MHz ROC (raid on a chip). Donâ€™t be fooled into thinking you can fit a cheap so called RAID card. They simple wonâ€™t solve the pausing and stuttering problem and the motherboards onboard SATA/RAID ports are simply not fast enough.
A PCIe x1 card is fine for a single SSD drive. If you want to add a second SSD and intend to have them setup in RAID 0 (stripped) then a PCIe x1 card wonâ€™t be fast enough. Remember a PCIe x1 lane has only 250MB/s bandwidth, without considering overheads.
What is really needed to allow a couple of fast SSD drives to breath and break free is a hardware RAID card with onboard cache and, using a PCIe x4 or x8 interface. With a fast ROC (raid on a chip) and 128MB of onboard cache and all importantly, using a PCIe x4 or x8 interface, you should have a around 1GB/s bandwidth on a x4 PCIe card and around 2GB/s bandwidth on a x8 PCIe card.
This may seem like overkill?
Well no, itâ€™s already becoming clear that SSD drives can very soon saturate a system bus. Remember, compared to a traditional hard drive, they have 10 to 30 times less reading latency. There is also no fall off in performance as the SSD read and writes, unlike a traditional hard drive where performance is really only fast for large files located at the start of the disc surface. When a traditional hard drive nears the centre of the spindle, performance can be only one third of the speed. SSD drives do not suffer from this; the reading and writing speed is equal throughout the drive.
SSD drives also scale much better than traditional hard drives in a RAID 0 configuration, having two traditional hard drives in RAID 0, does not give you anywhere near double the performance, whereas, adding two SSD drives in RAID 0 more or less doubles the performance, providing the RAID card is up to it.
Below is a result from a PCIe x1 hardware RAID card which simple canâ€™t cope with the amount of data these two SSD drives can supply.
The restriction on bandwidth on a single PCIe lane holds back the reading performance very badly. Now compare with the results of the same two drives on a x8 PCIe card (8 PCIe lanes).
Okay, letâ€™s see some results from a couple of MLC based SSD drives connected to a fast PCIe x8 hardware RAID card with onboard cache.
GigaByte GA-X48-DS4 (X48 chipset) motherboard
Intel Quad core CPU (Q6600) @2.4GHz
4 GB of OCZ Platinum PC6400 (4-4-4-15 timings)
Adaptec 2405 4 port unified hardware RAID, SAS/SATA (PCIe x8 interface).
Intel dual core ROC (raid on a chip) clocked at 800MHz.
128MB of write-back cache (DDR2 with parity checking).
Windows Vista Home Premium 64 Bit is installed and running from the SSD RAID setup.
2x 64GB OCZ Core V2 MLC drives in RAID 0
We will start off with a few benchmarks
HDTach reading performance test (large files 32MB zones)
282MB/s reading speed is very impressive.
Also note the access time of 0.3ms
Burst rate is also extremely good at 675.1 MB/s
HD Tune file benchmark (64MB file length)
OK itâ€™s very impressive, but really only showing the grunt of the RAID card when reading.
ATTO disk Benchmark (256MB file length)
This time we see the true file reading and writing performance of the SSD drives, as the file length is larger than the cache.
Reading speed tops out at 250MB/s and writing speed tops out at 200MB/s
So, how does the system feel and what is it like to use, using this SSD RAID setup?
Well, letâ€™s just say, it brings using the PC to a completely different levels. Applications load in an instant, saving large files in an instant and, all in complete silence.
So how much does this all cost?
Well it isnâ€™t cheap.
OCZ Core V2 64GB Â£129 each
Adaptec 2405 RAID card, around Â£179 (retail version)
Total = Â£437
I would really like to hear your views on this post and this setup, would you be prepared to spend this amount of money for this type of performance?
Do you have a traditional hard drive raid setup that can outperform this system? Letâ€™s see it.
Do you have an SSD drive yourself? Letâ€™s see some results.