Is it safe to use consumer MLC SSDs in a server?

A few thoughts;

• SSDs have 'overcommit' memory. This is the memory used in place of cells 'damaged' by writing. Low end SSDs may only have 7% of overcommit space; mid-range around 28%; and enterprise disks as much as 400%. Consider this factor.
• How much will you be writing to them per day? Even middle-of-the-range SSDs such as those based on Sandforce's 1200 chips rarely appreciate more than around 35GB of writes per day before seriously cutting into the overcommitted memory.
• Usually, day 1 of a new SSD is full of writing, whether that's OS or data. If you have significantly more than >35GB of writes on day one, consider copying it across in batches to give the SSD some 'tidy up time' between batches.
• Without TRIM support, random write performance can drop by up to 75% within weeks if there's a lot of writing during that period - if you can, use an OS that supports TRIM
• The internal garbage collection processes that modern SSDs perform is very specifically done during quiet periods, and it stops on activity. This isn't a problem for a desktop PC where the disk could be quiet for 60% of its usual 8 hour duty cycle, but you run a 24hr service... when will this process get a chance to run?
• It's usually buried deep in specs but like cheapo 'regular' disks, inexpensive SSDs are also only expected to have a duty cycle of around 30%. You'll be using them for almost 100% of the time - this will affect your MTBF rate.
• While SSDs don't suffer the same mechanical problems regular disks do, they do have single and multiple-bit errors - so strongly consider RAIDing them even though the instinct is not to. Obviously it'll impact on all that lovely random write speed you just bought but consider it anyway.
• It's still SATA not SAS, so your queue management won't be as good in a server environment, but then again the extra performance boost will be quite dramatic.

Good luck - just don't 'fry' them with writes :)

I did find this link, which has an interesting and thorough analysis of MLC vs SLC SSDs in servers

In my view using an MLC flash SSD array for an enterprise application without at least using the (claimed) wear-out mitigating effects of a technology like Easyco's MFT is like jumping out of a plane without a parachute.

Note that some MLC SSD vendors claim that their drives are "enterprisey" enough to survive the writes:

SandForce aims to be the first company with a controller supporting multi-level cell flash chips for solid-state drives used in servers. By using MLC chips, the SF-1500 paves the way to lower cost and higher density drives servers makers want. To date flash drives for servers have used single-level cell flash chips. That's because the endurance and reliability for MLC chips have generally not been up to the requirements of servers.

There is further analysis of these claims at AnandTech.

Additionally, now Intel has gone on the record saying that SLC might be overkill in servers 90% of the time:

"We believed SLC [single-level cell] was required, but what we found through studies with Microsoft and even Seagate is these high-compute-intensive applications really don't write as much as they thought," Winslow said. "Ninety percent of data center applications can utilize this MLC [multilevel cell] drive."

.. over the past year or so, vendors have come to recognize that by using special software in the drive controllers, they're able to boost the reliability and resiliency of their consumer-class MLC SSDs to the point where enterprises have embraced them for high-performance data center servers and storage arrays. SSD vendors have begun using the term eMLC (enterprise MLC) NAND flash to describe those SSDs.

"From a volume perspective, we do see there are really high-write-intensive, high-performance computing environments that may still need SLC, but that's in the top 10% of even the enterprise data center requirements," Winslow said.

Intel is feeding that upper 10% of the enterprise data center market through its joint venture with Hitachi Global Storage Technologies. Hitachi is producing the SSD400S line of Serial Attached SCSI SSDs, which has 6Gbit/sec. throughput -- twice that of its MLC-based SATA SSDs.

Intel, even for their server oriented SSD drives, has migrated away from SLC to MLC with very high "overprovisioning" space with the new Intel SSD 710 series. These drives allocate up to 20% of overall storage for redundancy internally:

Performance is not top priority for the SSD 710. Instead, Intel is aiming to provide SLC-level endurance at a reasonable price by using cheaper eMLC HET NAND. The SSD 710 also supports user-configurable overprovisioning (20%), which increases drive endurance significantly. The SSD 710's warranty is 3 years or until a wear indicator reaches a certain level, whichever comes first. This is the first time we've seen SSD warranty limited in this manner.