[ltp] Re: solid state drive?

[Theodore Tso]

On Tue, Feb 17, 2009 at 12:45:12AM +0200, Micha Feigin wrote:
> 
> That is because the op asked about cheap SSDs. There was a thread
> somewhere on one of the mailing lists I'm registered to, can't
> remember at the moment which one. Apparently IIRC there are two
> technologies for SSD. The cheap one that is probably in the EeePC
> which is very slow to write and has a life span of about 10000 write
> cycles and the expensive one (a 80gb costs about as much as the
> whole EeePC) which is fast (at least on par to regular disk) and has
> a life cycle of around 100000+ writes.

You're talking about first generation MLC vs. SLC flash drives; it
turns out though that with the right smarts, though, it's possible to
make MLC flash work well.  See this article from Tom's Hardware:

    http://www.tomshardware.com/reviews/Intel-x25-m-SSD,2012-3.html

Intel was the first to market by about 4-5 months; however, San Disk
is supposed to come out with a drive with similar "smarts" in the next
month or two.  I can't say anything about how well San Disk's drive
will work, since I haven't seen any early reviews yet and I haven't
been able to get early access to the drive, but the reviews from
Intel's SSD (which is ground-breaking) have been glowing.

As far as prices are concerned, the Intel X25-M SSD is more expensive
than traditional MLC drives, but cheaper than SLC drives.  The street
price of the 80GB SSD is $400.  Sure, that's about 4x the price of an
HDD, but given its shock resistance and speed, that's not bad.  In
contrast, traditional 64GB SLC drives cost about $500, and traditional
64GB MLC drives cost about $140.  (And an 80GB HDD is about $40).

     	 	     	   	       - Ted

P.S.  Note that if you are doing streaming writes, the Intel X25-M
isn't going to be that much faster than an traditional MLC, because
it's using MLC flash.  The reason why Intel's SSD is better is because
in real life it's rare that the OS will be able to do streaming
writes; instead it needs to do a number of small writes to update the
inode table, allocation bitmaps/tables, etc. for each file writes (and
many files are small to begin with).  What makes the Intel SSD
interesting is that it has better smarts that means that a more
realistic, real-world workload that has lots of small writes still
works relatively well on the X25-M, whereas on a traditional MLC drive
write amplification means that it has to erase and write an 128k block
even when updating a 4k block.  That means that for small writes, a
traditional MLC drive will take a factor of 16-32 hit off of its
sequential write speeds, and factor 16-32 times increase in flash
lifetime (since 128k is getting erased and rewritten even for a 4k
write).