SLOG Latency
After reading Brendan's newest blog entry, I was curious about what kind of slog latency we can see for our data migration load.
To remind you, only synchronous writes go into the slog SSD devices.
As this is a migration running, we can see mostly NFS write operations:
In our configuration the SSD slog is mirrored (HDD4 and HDD8). Hence the same number of IOPS:
The next picture shows us the latency for our SDD SLOG Device HDD 4. We can see here that latencies start at 79 us and are mostly under 200 us. There are some outliers, but approx. 95% are under 500 us:
This matches quite well with the values Brendan blogged about (137-181 us), which includes NFSv3 latency. For reference (no picture here), we can see latencies of about 170-500 us mostly for NFSv4.
By the way. SLOG Devices are mostly one way devices, as shown here. Only if things go really bad, they are read from...
To remind you, only synchronous writes go into the slog SSD devices.
As this is a migration running, we can see mostly NFS write operations:
In our configuration the SSD slog is mirrored (HDD4 and HDD8). Hence the same number of IOPS:
The next picture shows us the latency for our SDD SLOG Device HDD 4. We can see here that latencies start at 79 us and are mostly under 200 us. There are some outliers, but approx. 95% are under 500 us:
This matches quite well with the values Brendan blogged about (137-181 us), which includes NFSv3 latency. For reference (no picture here), we can see latencies of about 170-500 us mostly for NFSv4.
By the way. SLOG Devices are mostly one way devices, as shown here. Only if things go really bad, they are read from...
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