Potential Issues
I have a couple points of issue with using SSDs for production databases at the present time
- The majority of database transactions on a the majority of websites are reads not writes. As Dave Markle said, you maximize this performance with RAM first.
- SSDs are new to the mainstream and enterprise markets and no admin worth his salt is going to move a production database that currently requires 15K RPM U320 disks in RAID5 communicating via fibrechannel to an unproven technology.
- The cost of the research and testing of moving to this new technology, vetting it in their environment, updating the operating procedures, and so forth is a larger up front cost, both in terms of time and money, than most shops have to spare.
Proposed Benefits
That said, there are a number of items, at least on paper, in favor of SSDs in the future:
- Lower power consumption compared to a HDD
- Much lower heat generation
- Higher performance per watt compared to a HDD
- Much higher throughput
- Much lower latency
- Most current generation SSDs have on the order of millions of cycles of write endurance, so write endurance is not an issue as it once was. See a somewhat dated article here
So for a given performance benchmark, when you factor total cost of ownership including direct power and indirect cooling costs, the SSDs could become very attractive. Additionally, depending on the particulars of your environment, the reduction in the number of required devices for a given level of performance could also result in a reduction of staffing requirements, reducing labor costs.
Cost and Performance
You've added that you have a cost constraint under $50K USD and you really want to keep it under $10K. You've also stated in a comment that you can get some "cheap" SSDs, eluding that the SSDs will be cheaper than the DBAs or consultants. This may be true depending on the number of hours you would need a DBA and whether it is a reoccuring cost or not. I can't do the cost analysis for you.
However, one thing you must be very careful of is the kind of SSD you get. Not all SSDs are created equal. By and large the "cheap" SSDs you see for sale in the $200-400 dollar (2008/11/20) are intended for low power/heat environments like laptops. These drives actually have lower performance levels compared to a 10K or 15K RPM HDD - especially for writes. The enterprise level drives that have the killer performance you speak of - like the Mtron Pro series - are quite expensive. Currently they are around:
- 400 USD for 16GB
- 900 USD for 32GB
- 1400 USD for 64GB
- 3200 USD for 128GB
Depending on your space, performance, and redundancy requirements, you could easily blow your budget.
For example, if your requirements necessitated a total of 128GB of available storage then RAID 0+1/10 or RAID 5 with 1 hotspare would be ~$5600
If you needed a TB of available storage however, then RAID 0+1/10 would be ~$51K and RAID 5 with 2 hotspares would be ~$32K.
Big Picture
That said, the installation, configuration, and maintenance of a large production database requires a highly skilled individual. The data within the DB and the services provided from that data are of extremely high value to companies with this level of performance requirements. Additionally, there are many things that just cannot be solved by throwing hardware at the problem. An improperly configured DBMS, a poor database schema or indexing strategy can /wreck/ a DB's performance. Just look at the issues Stackoverflow experienced in their migration to SQL Server 2008 here and here. The fact of the matter is, a database is a strenuous application on not only disk but RAM and CPU as well. Balancing the multi-variate performance issue along with data integrity, security, redundancy, and backup is a tricky bit.
In summary, while I do think any and all improvements to both the hardware and software technology are welcomed by the community, large scale database administration - like software development - is a hard problem and will continue to require skilled workers. A given improvement may not reap the labor reduction costs you or a company might hope for.
A good jumping point for some research might be Brent Ozar's website/blog here. You might recognize his name - he's the one who has assisted the stackoverflow crew with their MS SQL Server 2008 performance issues. His blog and resources he links to offer quite a bit of breadth and depth.
Update
Stackoverflow themselves are going the consumer SSD-based route for their storage. Read about it here: http://blog.serverfault.com/post/our-storage-decision/
References
A self-speaking excerpt from man mdadm:
-W, --write-mostly
subsequent devices listed in a --build, --create, or --add command will be flagged as 'write-mostly'. This is valid for RAID1
only and means that the 'md' driver will avoid reading from these devices if at all possible. This can be useful if mirroring
over a slow link.
Best Answer
The use-case here is flawed. The one use-case where this makes sense is where your I/O activity is majority-read by a very large degree (like 9:1). In that case, since there are so few writes the HD can keep up with the changes coming from the SSD. If the ratio is any less then that, then the SSD risks outpacing the HD's entire write ability.
What you're looking at isn't RAID, it's replication. Something like drbd is what you're looking for. The system will keep a delta-cache of writes to commit to the HD, and periodically flush those writes to the HD. But as I said, since an SSH can handle w-a-y more writes than an HD can, this only works if you're doing very little writing to the SSD.