IBM blade server abysmal disk write performances

[Wojciech Puchar]

>
> The default value, -1, instructs the driver to leave the STA drives at their configuration default.  Often times this means that the MPT BIOS will turn off the write cache on every system boot sequence.  IT DOES THIS FOR A GOOD REASON!  An enabled write cache is counter to data reliability.  Yes, it helps make benchmarks look really good, and it's acceptable if your data can be safely thrown away (for example, you're just caching from a slower source, and the cache can be rebuilt if it gets corrupted).  And yes, Linux has many tricks to make this benchmark look really good.  The tricks range from buffering the raw device to having 'dd' recognize the requested task and short-circuit the process of going to /dev/null or pulling from /dev/zero.  I can't tell you how bogus these tests are and how completely irrelevant they are in predicting actual workload performance.  But, I'm not going to stop anyone from trying, so give the above tunable a try
> and let me know how it works.
>
If computer have UPS then write caching is fine. even if FreeBSD crash, 
disk would write data