Hp StorageWorks Scalable File Share Bedienungsanleitung PDF herunterladen (Seite 61)

Figure A-3 shows single stream performance for a single process writing and reading a single 8

GB file. The file was written in a directory with a stripe width of 1 MB and stripe count as shown.

The client cache was purged after the write and before the read.

Figure A-3 Single Stream Throughput

For a file written on a single OST (a single RAID volume), throughput is in the neighborhood of

200 MB per second. As the stripe count is increased, spreading the load over more OSTs,

throughput increases. Single stream writes top out above 400 MB per second and reads exceed

700 MB per second.

Figure A-4 compares write performance in three cases. First is a single process writing to N OSTs,

as shown in the previous figure. Second is N processes each writing to a different OST. And

finally, N processes to different OSTs using direct I/O.

Figure A-4 Single Client, Multi-Stream Write Throughput

For stripe counts of four and above, writing with separate processes has a higher total throughput

than a single process. The single process itself can be a bottleneck. For a single process writing

to a single stripe, throughput is lower with direct I/O, because the direct I/O write can only send

one RPC to the OST at a time, so the I/O pipeline is not kept full.

For stripe counts of 8 and 16, using direct I/O and separate processes yields the highest throughput.

The overhead of managing the client cache lowers throughput, and using direct I/O eliminates

this overhead.

A.2 Single Client Performance 61

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Hp StorageWorks Scalable File Share Bedienungsanleitung Seite 61