Dell PowerVault MD1200 - Manual (Page 19)

Improving NFS Performance on HPC Clusters with Dell Fluid Cache for DAS
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better than the baseline since the data is already in the DFC cache. As expected on read operations,
WB and WT tests have similar performance and can reach peak throughout of ~3050 MiB/s.
3.2. Random writes and reads
Figure 7 plots the aggregate IOPs when a number of clients are simultaneously issuing random writes to
their files. The baseline configuration can sustain ~1,600 IOPs on writes. Random writes are limited by
capability of the RAID controller and the disks seek latency of the backend disks.
With DFC in WB mode, the true value of DFC becomes apparent. Write IOPs are up to 6.4 times higher
(6.4x) than the baseline configuration at 64 clients. In random write tests, the cache warms up very
quickly since random operations tend to be ‘small’ with a 4k block size. In WT mode, DFC behavior and
performance is similar to the baseline as all writes go through to the backend disk.
Figure 8 plots the aggregate read IOPs when a number of clients are simultaneously issuing random
read operations. The baseline configuration sustains ~9,300 IOPS. As expected on read operations, DFC
WB and WT tests have similar performance and peak at 123,000 IOPs at 32 clients! That is over 20x
higher than the baseline performance.
Clearly read requests are being fulfilled from the DFC cache and that is the value of such caching
software. The question that arises is about worst case read performance. What is the drop in
performance when the data is accessed after it has been evicted from the cache? This scenario is
explored in Section 3.4.
Random write performance Figure 7.
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