The SSD Relapse: Understanding and Choosing the Best SSD
by Anand Lal Shimpi on August 30, 2009 12:00 AM EST- Posted in
- Storage
Sequential Read/Write Speed
Finally, to the roundup. We’ll start with the traditional tests. Using the latest build of Iometer I ran a 3 minute long 2MB sequential write test over the entire span of the drive. The results reported are in average MB/s over the entire test length:
Sequential write speed was what all SSD makers focused on in the early days of consumer drives. The JMicron lesson taught us that there's much more to system performance than sequential write performance, and most have learned. Regardless, sequential write speed is still very important and as we can see here the majority of drives do very, very well. The high end Indilinx drives approach 190MB/s, while Intel's SLC X25-E actually breaks 200MB/s.
The same can't be said for Intel's mainstream MLC drives, both of which are limited to 80MB/s. While it doesn't make the drives feel slow in real world usage, it is a significant blemish on an otherwise (as you'll soon see) flawless track record.
The standings don't really change with the drive in a used state. The Indilinx drives all fall around 15%, while the Intel drives stay the same.
Ha! Read speed is ridiculous on these drives. See the wall at around 260MB/s? We're hitting the limit of what's possible over 3Gbps SATA. Expect read speeds to go up once we start seeing SATA 6Gbps drives and controllers to support them.
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Anand Lal Shimpi - Monday, August 31, 2009 - link
The tables the drive needs to operate are also stored in a small amount of flash on the drive. The start of the circular logic happens in firmware which points to the initial flash locations, which then tells the controller how to map LBAs to flash pages.Take care,
Anand
Bakkone - Monday, August 31, 2009 - link
Any gossip about the new SATA?Zaitsev - Monday, August 31, 2009 - link
Thanks for the great article, Anand! It's been quite entertaining thus far.cosmotic - Monday, August 31, 2009 - link
The page about sizes (GB, GiB, spare areas, etc) is very confusing. It sounds very much like you are confusing the 'missing' space when converting from GB to GiB with the space the drive is using for its spare area.Is it the case that the drive has 80GiB internally, uses 5.5GiB for spare, and reports it's size as 80GB to the OS leaving the OS to say 74.5GiB as usable?
Anand Lal Shimpi - Monday, August 31, 2009 - link
I tried to keep it simply by not introducing the Gibibyte but I see that I failed there :)You are correct, the drive has 80GiB internally, uses 5.5GiB for spare and reports that it has 156,301,488 sectors (or 74.5GiB) of user addressable space.
Take care,
Anand
sprockkets - Tuesday, September 1, 2009 - link
Weird. So what you are saying is, the drive has 80Gib capacity, but then reports it has 80GB to the OS, advertised as having an 80GB capacity, which the OS then says the capacity is 74.5GiB?sprockkets - Tuesday, September 1, 2009 - link
As a quick followup, this whole SI vs binary thing needs to be clarified using the proper terms, as people like Microsoft and others have been saying GB when it really is GiB (or was the GiB term invented later?)For those who want a quick way to convert:
http://converter.50webs.com">http://converter.50webs.com
ilkhan - Monday, August 31, 2009 - link
so they are artifically bringing the capacity down, because the drive has the full advertised capacity and is getting the "normal" real capacity. :argh:Vozer - Monday, August 31, 2009 - link
I tried looking for the answer, but haven't found it anywhere so here it is: There are 10 flash memory blocks on both Intel 160GB and 80GB X25-M G2, right? (and 20 blocks with the G1).So, is the 80GB version actually a 160GB with some bad blocks or do they actually produce two different kind of flash memory block to use on their drives?
Anand Lal Shimpi - Monday, August 31, 2009 - link
While I haven't cracked open the 80GB G2 I have here, I don't believe the drives are binned for capacity. The 80GB model should have 10 x 8GB NAND flash devices on it, while the 160GB model should have 10 x 16GB NAND flash devices.Take care,
Ananad