We use it for both, but most commonly we use it to compare a single metric (such as CPU or network utilization) across hosts.
Line graphs work well when you only have a few hosts, but start to suffer when you try to plot many hosts simultaneously. Depending on how noisy your metrics are, line graphs are good for showing the envelope, but are less effective at revealing when one or two hosts are behaving oddly; the anomalies get lost in the mess of lines. (It doesn't help that the default colors in Graphite are bad; the host that happens to be assigned bright yellow against a white background becomes much harder to see.)
Small multiples give each host a dedicated row, so you don't have to worry about occlusion or distraction. However, that requires more vertical space, which is why you need horizon graphs or a similar technique to compress them. Scrolling with a vertical rule also helps detect coincident anomalies across metrics.
Thanks for the insight. I hadn't seen horizon graphs previously, they're interesting and a great way to compact data and in a way that maintains readability.
Regarding line graphs, there is some visibility loss by having a a single line graph show a ton of servers. I tend to think that deviations that are worth noting tend to stick out. That isn't always going to be the case I suppose, but nothing is 100%.
I'm just not sure how this scales if I've got 100 servers with 2-3 metrics each that I'm tracking. Perhaps this is better for more of a detailed view than a dashboard where where more density is needed. They're certainly more readable then what we use today.
Line graphs work well when you only have a few hosts, but start to suffer when you try to plot many hosts simultaneously. Depending on how noisy your metrics are, line graphs are good for showing the envelope, but are less effective at revealing when one or two hosts are behaving oddly; the anomalies get lost in the mess of lines. (It doesn't help that the default colors in Graphite are bad; the host that happens to be assigned bright yellow against a white background becomes much harder to see.)
Small multiples give each host a dedicated row, so you don't have to worry about occlusion or distraction. However, that requires more vertical space, which is why you need horizon graphs or a similar technique to compress them. Scrolling with a vertical rule also helps detect coincident anomalies across metrics.