Dell PowerEdge M420 Manuel - Page 19

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Improving NFS Performance on HPC Clusters with Dell Fluid Cache for DAS

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.

14000

12000

10000

8000

6000

4000

2000

Figure 7.

Random write performance

Random writes

Number of concurrent clients

baseline

DFC-WB

DFC-WT