The Changing Solid State Drive Landscape
Major transitions are in progress in the solid state drive (SSD) area. Within about 10 weeks, these transitions should be complete.
There is always something faster in the computing world. But theoretically faster is not always actually faster in the real world for many tasks, so an SSD solution you need now is already available, and excellent. Remember also that SSDs proven for a year have some value over new and unproven models.
Cost reduction with flash memory chip transition to 25nm
The 25nm transition is already driving down flash memory prices substantially.
Already, OWC is offering a 400GB SSD for about $920, down from about $1600 for its previous 480GB model. Smaller capacity devices will see less compelling percentage price drops.
In general, the 25nm chips require more over provisioning for reliable long term use, so we will see 115GB instead of 120GB, 230GB instead of 240GB capacity, etc.
Over provisioning is why a drive with 512GB of flash memory has a usable capacity of 400GB or 480GB, depending on its intended use— the set-aside is for long term reliability to compensate for failed flash cells, which occurs even with Tier 1 flash memory.
Performance from 32nm to 25nm flash memory chips
The 25nm change might drop performance slightly on some devices, but that is an open question to be evaluated when a full product lineup emerges, and newer firmware might mitigate that issue.
6Gbps SATA III devices from 3Gbps SATA II devices
The OWC Mercury Extreme Pro line of solid state drives are good for about 270MB/sec reads and 250MB/sec writes with a SATA 3G port. Speeds can be much lower with highly compressed (random) data, though real-world tasks rarely see that kind of impact.
Assuming a SATA III 6Gbps port and a future OWC SSD that we can assume has to appear with the 2nd generation Sandforce controller, speeds should hit as high as 500MB/sec for compressible data, and be about as fast with random data as the 3G drives are at their peak. In other words, a 6Gbps Sandforce-based SSD should provide roughly the same performance as two 3Gbps SSDs in a RAID-0 stripe.
This all sounds good, but the Apple Mac Pro still has only SATA 3Gbps ports (but see notes on the OWC PCIe card below). The 2011 Apple MacBook Pro has one (1) SATA III 6Gbps port.
Even though a 6Gbps SSD on a 6Gbps SATA III port is theoretically much faster, it would be foolish to assume real-world performance commensurate with that difference— much of the SSD advantage is also about the minimal latency and fast request handling, so many performance gains are already baked-in with existing SSDs.
Don’t assume that new any Brand X SSD is compatible.There are always growing pains. I will be testing new models as soon as they are available.
I recommend waiting for vendors like OWC to officially release product they have tested and certified as Mac compatible.
Strategy for SSDs
Costs are dropping substantially on SSDs, especially larger capacity models, and peak (test) performance will just about double within two months.
Most Macs do not have a 6Gbps SATA III port, and most real world usage will see little or no benefit. So if you need an SSD now, get one, because most of the gains to be had are already baked in— the law of diminishing returns sets in with the majority of software programs.
Another strategy is to get a smaller SSD now, the get a higher capacity 6Gbps model after prices have dropped.
In a few specialty situations, the newest 6Gbps SSDs will be helpful. Users with extreme performance demands might put off purchase of the high capacity SSDs for 8-10 weeks, and work for now with existing 3Gbps SSDs of lower capacity.
Mac Pro users
For Mac Pro users that require supreme speed and/or high capacity, the OWC PCIe SSD card will provide an absurd amount of I/O bandwidth with 6Gbps SSDs, eclipsing any standard SATA port solution on the Mac Pro. Presumably this card will appear sometime shortly after 6Gbps SSDs are shipping— or so I hope.
MacBook Pro users
The 2011 Apple MacBook Pro has one (1) 6Gbps port. Users seeking top performance might want to migrate to a 6Gbps SSD when available, using a smaller capacity one in the interim.
iMac, MacMini users
Price is the main driver here— any current SSD will be a big step up over the supplied hard drive. Neither the iMac nor the MacMini has SATA 6Gbps as this was written.