Performance Engineer John L. Henning shares why he has lost his fear of ZFS since many of his previous concerns have been resolved as the technology has improved over time, and he has learned more about using the Sun file system. SPEC CPU benchmarks and IO are areas that he previously had some trepidations about, and another was the consumption of memory that ZFS had been rumored to make. In an article posted on his blog, he shows why he can now embrace the features of ZFS.

SPEC CPU Benchmark and IO

The reason this issue was of concern for Henning was time. He relates that with the use of an internal drive (Seagate ST973402SSUN72G), a T5220 with a Niagara 2 processor would read the 1/4 GB file at about 50 MB/sec and about 5.5 seconds is used to read one copy of the file. Now, take into account running one copy of the actual benchmark or about 3000 seconds. That is a lot of time. Additionally, 1/4 GB becomes an issue since performance engineers read more than one copy of the file when testing SPEC CPU2006. This is because the interest for them lies in the SPECrate metrics, which run multiple copies of the benchmarks.

He provides a graphed example of an M5000 that shows approximately 18 minutes before the CPU reaches the desired 99% user time. During that 18 minutes, a single disk with ufs on it is, according to iostat, 100% busy. It reads about 16 MB/sec, doing about 725 reads/sec. This translates to idle CPU time, which is not good for a CPU benchmark.

Then he introduces ZFS and its compression feature, which can eliminate 90% of the IO. The test is run once again with the specific goal to drive user time to 100% as quickly as possible. The graph shows an almost immediate desired result.

Memory Consumption

Henning describes in some length the relationship between ZFS and memory. His example here is a 4-chip T5440. One important lesson to note is that ZFS will indeed use all the memory on the system if it thinks it can get away with it, he writes. Therein lies the answer - tuning ZFS to not hog memory.

Other basic lessons about ZFS Henning passes along:

• Selecting gzip compression can be a big win, especially on systems with relatively faster CPUs.

• Setting up mirrored drives with dynamic striping is straightforward.

• Bottom-line: ZFS is not so scary, after all.

More Information

Losing My Fear of ZFS - Henning's article

The ZFS Guides

BigAdmin: ZFS

Solaris ZFS Product Page

SPEC CPU benchmarks [...read more...]

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