Like I said , ssd is still faster than ssd+hd. So if you want performance you still want ssd. If you want capacity you still want hd. So, what stopping you to buy one ssd and one hd and put in computer.
How many type of this ssd+hd do they have in market.
Even if all hdd is hybrid, I still want ssd for my os.
These are different strategies. Seagate's rice-bowl is still Winchester HDD and they have much interest to defend this territory. Western Digital however have SSD products. But I am now not talking about market strategies of these makers, just mentioning their relevant backgrounds. I am talking about user's strategies for performance and cost, using these makers products.
A pure SSD device for OS is a strategy. I will recommend it for performance workstations that shuts down frequently, and critical servers that must come back to life ASAP. To make performance servers or workstations fast these days, you should consider to virtualize them and use the performance of VDISKS/RAM DISKS, many additional advantages of virtual machines applies. Linux OS easily fit into few GB of image foot-print. I configured OS partitions like 15GB with lots of rooms to spare still. 8GB of VDISK using RAMFS can boot many systems up, workstations need more space than servers typically.
Your boot image is copied from SAN/RAID to RAMFS before starting the virtual machine mount as /. Then you mount on /home /var /srv etc from SAN or RAID. One advantage e.g. during maintenance or upgrade of hardware you can suspend the virtual server and quickly copy from one RAMFS to another physical server's RAMFS, and resume serving, you don't even have to shut down and your server already changed from one box into another, flying through highspeed LAN.
We come back to this hybrid flash cached HDD, it is a HDD with enhancement as a strategy of use. It may be your data disk if not OS or both together. To those home / office PCs these are just improved HDDs with just few dollar more worth of (4GB) flash. It is not quite comparable against few hundred bugs SSD, in prices & capacities.
Like I posted here earlier, I surely won't expect it's performance to be SSD when I format the whole thing or defrag it, that is because these operations will surely saturate the capacity of 4GB cache. There is also a point that these drives require less defrag because it is a quasi SSD. Doing defrag on SSD is quite a waste of time, only to make file tables more orderly/sequential.
On the other hand, cache RAM had been constantly on the increase on HDD, for commercial HDD reached 64MB now. The introduction of flash cache may change this picture. Eventually, there will be a logical ration between the capacities of Winchester & flash & RAM caches.
I also foresee that flash cache will be introduced within SAN / RAID / NAS, I am not referring to inside the individual disk elements, but inside the appliance itself, a layer between their existing RAM cache and their disk elements. Some SCSI controllers themselves have got onboard battery-backed RAM cache already, flash does not need batteries. So while replacing these RAID boards, you can just physically transfer their RAID modules from old RAID cards to new RAID cards.
Example : Apple / Dell / HP
http://reviews.cnet.com/i-o-cards/apple-mac-pro-raid/1707-3019_7-32742022.html
RAID engine, 256MB of cache, and an integrated 72-hour battery for protecting cache data.
