Need Assistance with PC Specs

Started Jun 13, 2013 | Discussions thread
kelpdiver Veteran Member • Posts: 3,614
Re: faster speeds with larger SSDs

Jim Cockfield wrote:

When looking at smaller consumer mlc based SSDs, they're slower (especially on the write side).

There is a little truth here, but wrapped inside a terribly inaccurate generalization.

Most SSDs have 8 channels of memory (Intel instead does 10).  The smallest capacity drive may only have 4 channels, and that can make a marked difference to the claimed performance metrics.  This used to be a problem for the 60gb units.  The M4 64gb was substantially slower in writes than the 120/240/480.  Note that it looked like the 480 was too big and suffered as a result - lot of negative reports.

with the newer M500, the densities doubled the 128gbit dies and now the 128G is the lower performer on writes, with a claimed 130MB/s versus 250/400 for the bigger ones.  IOPS is also down, but no desktop user is going to care - the queue depths aren't that high.

The 840 pro also has only 4 channels for the 128, but I suspect the use of dram memory blunts the difference as it is only 20% slower than the 8 channel offerings.

You always will have to look at the particular models.  My 64gig M4 beat up my 128gb Vertex 2...badly, even if it trailed its bigger capacity m4s.  You have to look at the figures and unfortunately it's not always immediately visible if a particular model has 4 or 8 channels, or 8 on each side of the PCB board.

Not only are larger SSDs faster, their life expectancy is much longer (256GB or larger SSDs are rated for many more p/e cycles compared to smaller models).

Now you're making stuff up.   P/E cycles are largely based on the manufacturing density.  Each time they go to a small process (which enables higher capacity), the p/e rating has declined.  The older less dense memory chips had higher endurance.  Back when we still were afraid of write endurance bogeyman, a lot of people were upset at the change from 34nm to 25nm, and the 40% decline in p/e cycles.

So, I'd definitely avoid using 128GB SSDs just to split out i/o, as I think you'd see better overall performance by sticking with 256GB or larger SSDs instead, especially given the lower latency you see with modern SSDs now.

IOW, the performance bottlenecks you see with smaller SSD models is likely to be greater than the benefits of splitting i/o between multiple drives, given the lower latency you see with SSDs anymore.

To reiterate, the reason for a separate OS drive was not about performance, it was about separating static content (OS + apps) from data.  If you just want to make a system image, you don't want to back up the data.  If you want to try a different OS or upgrade, pull the current OS disk, insert the new one, and go at it.  If you want to back out, you just put in the original drive.  But when you have multiple drives with Windows installed on a system, I get worried that Redmond is going to screw things up.  I'm sure you've encountered it going after non windows OS installs in the past.

And let's be honest - the OS/app disk is largely a write one drive.   Read performance is what matters to the user experience.  The install process is limited by the the speed of the dvd and the cpu, so there may or may not be an actual penalty in the install.  But the read speeds do not usually differ at all between the different capacities of a model line.   For the samsung 840 pro, the 128 writes at 390 instead of 520.  It still reads at 540.  I'm sure some synthetic tests can amplify that difference, but real world results...little difference.  Not enough to override any organizational planning.

Again, personally, I'd go with a single larger SSD instead. You'd get faster throughput that way (especially for writes), without the hassles associated with trying to segment data between multiple drives, and you'd probably get a better price/performance (GB/Dollar) ratio, too.

And to repeat again, the GB/dollar doesn't vary much.  The 480s cost roughly twice the 240s which are roughly the 120s.  When there is a sale, you see some inflection points that may favor a particular size over the others.  For quite some time, the 480/500G class commanded a premium price.  That is likely true now for the 960/1tb class as people are clamoring to remove physical drives entirely.

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