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73796
May 15th, 2013 01:00
Maximum data transfer rates for each SATA port ... and SSD caching considerations
I did not notice before today that the internal SATA storage devices are a mixture of 6Gb/s, 3Gb/s and 1.5Gb/s data transfer rates. I only discovered this as I was studying the advanced detail displayed by the iRST (Intel Rapid Storage Technology) application.
Now that I have read the Intel HM77 Express chip set product brief I can better understand why this is so (support for up to 2 SATA III 6Gb/s ports and up to 4 SATA II 3Gb/s ports) however, I don't yet think that I fully understand my internal storage options for the Inspiron 7720; and so I have a few questions for anybody who has looked into this already:
- What is the maximum SATA data transfer rate for each of these ports? [assumption based on my limited observations]
a) Port 0 : the SATA socket where a System HDD is installed [up to 6Gb/s]
b) Port 1: the SATA socket where a Data HDD is installed (if your model came with a second HDD) [probably up to 6Gb/s]
c) Port 2: the mSATA socket where an SSD cache for the HDD is installed [up to 3Gb/s]
d) Port 3: the SATA socket where an ATAPI optical drive (Blu-ray and/or DVD drive) is installed [probably up to 3Gb/s] - What devices use the remaining two SATA II ports? Or are there just the above 4 SATA ports?
[I assume that "up to 4 SATA II ports" really means that two SATA III ports can be under-utilized as two SATA II ports.] - The iRST application reports the SATA transfer rate for the mSATA 32GB SSD is 3Gb/s. The data sheet for the Samsung SSD PM830 mSATA 32GB clearly specifies that it is 6Gb/s capable and hence my [assumption] above.
Is there any complication or compromise to be expected if a 6Gb/s SSHD is cached using an SSD on this 3Gb/s mSATA port?
Specifically,
If a SATA III (6Gb/s) SSHD (Solid-state hybrid drive) is used on Port 0 or Port 1 then is hard disk write/read performance going to be best if that 6Gb/s drive is not cached using a 3Gb/s mSATA SSD?
(Without considering the independent benefit from Intel Rapid Start Technology i.e. saving the hibernate state of the installed 8GB system memory.) - Is iRST able to use the integrated SSD cache of an SSHD on port 0 or port 1? [I assume No.]
Specifically,
Can Intel Rapid Start Technology save the hibernate state of the installed 8GB system memory on the integrated SSD cache of an SSHD using port 0 or port 1? - If an optical drive bay caddy is used to install a HDD in place of the Blu-ray/DVD drive then will a SATA III drive be under-utilized on port 3?
[I assume yes.] - What is the reasoning behind the Inspiron 7720 being configured with SATA II (3Gb/s) HDDs rather than SATA III (6Gb/s) HDDs?
I hope that the answers to these question prove helpful to other readers considering this laptop.
osprey4
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34.2K Posts
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May 15th, 2013 16:00
Hi ChrisB,
It's not clear if you own this model or are shopping, but let me know.
For rotational drives, it makes no difference whether the drive is SATA II or III. The actual data transfer rate is considerably slower than the theoretical SATA standard. The better configuration is an SSD primary drive over the cache. You won't use both. Obviously, if you go with an SSD primary drive, it should be SATA III, which will make a difference.
As far as how many ports, I assume there are two for hard drives and one for the optical drive. If you need more than that, I'd recommend a desktop.
cjfb
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May 17th, 2013 00:00
Osprey,
Many thanks. Your reply prompted me to do further research and so now I do appreciated how 8b/10b encoding gives rise to 600:300:150 MB/s transfer rates for SATA III:II:I respectively. It makes a lot of sense to discuss this subject in terms of MB/s realized data transfer rates rather than raw Gb/s capability.
A closer inspection of the data sheets for the SSD, HDD and SSHD referred to in my original post confirms the relatively slow throughput rates that you outlined with one additional surprise from the SAMSUNG SSD PM830 mSATA 32GB device:
mSATA 32GB SSD on port 2:
1TB HDD on port 1:
1TB SSHD on port 0:
The devil really is in the detail. Transfer rates to/from a drive's DRAM buffer mean very little in real world situations yet feature prominently in the marketing propaganda for each drive! I can very well understand why SATA-II HDD's were selected for this product.
I did learn that Intel Rapid Start software does store the hibernate state of 8GB system memory on the specified mSATA SSD cache regardless of whichever storage device is selected for acceleration by Intel Rapid Storage software. So the rapid resume benefit can be enjoyed regardless of whichever drive is chosen for acceleration.
Yes, I very recently purchased the Inspiron 17R SE described in my signature.
osprey4
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34.2K Posts
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May 17th, 2013 11:00
To clarify the situation with your two hard drives, this is not a problem with the SATA ports. All mechanical drives are much slower than allowed by the SATA port. Even an SATA III hard drive is going to be slow.
However, the cache performance might improve using an SATA III SSD. You might want to send that query to Dell. It seems to me an SATA III port should be equipped with an SATA III SSD cache.