And to add a bit more context: - The RAM Cache is highly related to the Disk Cache and physical disks -- as you surmise, the disk cache would need to be at least as big as the RAM cache. - BUT, as Kit and Rob mention, RAM Disks are a neat cheat -- ATS thinks of them as a disk cache. If you are exclusively running with RAM Disks, you should likely set proxy.config.cache.ram_cache.size (in records.config) to nil ( https://docs.trafficserver.apache.org/en/8.1.x/admin-guide/files/records.config.en.html#proxy-config-cache-ram-cache-size). I believe the feature Kit refers to is new in ATS 9, and is more focused on the mixed case (for instance, we run both RAM Disk and physical disks -- the RAM Cache associated with the RAM disk unnecessarily wastes memory). miles
On Wed, Apr 7, 2021 at 12:24 PM Shu Kit Chan <[email protected]> wrote: > I also used RAM disk as well. And one thing I will try is to disable the > ram cache of ATS - > https://docs.trafficserver.apache.org/en/latest/admin-guide/storage/index.en.html#disabling-the-ram-cache > > > I think that will then make it a bit more straightforward to reason about > the whole situation. > > Kit > > On Wed, Apr 7, 2021 at 10:04 AM Nick Dunkin <[email protected]> > wrote: > >> Hi Rob, >> >> >> >> This is excellent information, thank you very much. >> >> >> >> I had considered a large RAM cache setting (ram_cache) with just a small >> disk cache, but the ATS documentation was very vague about what this would >> mean. The documentation refers to the ram cache as a place where popular >> items are *promoted*, inferring (to me at least) that the size of the >> disk cash would always have to be larger than the ram cache, in order make >> full use of the ram cache. >> >> >> >> As you say though, I prefer the RAM disk path. >> >> >> >> Thanks again, >> >> >> >> Nick >> >> >> >> *From: *Robert O Butts <[email protected]> >> *Reply-To: *"[email protected]" < >> [email protected]> >> *Date: *Wednesday, April 7, 2021 at 12:54 PM >> *To: *"[email protected]" <[email protected]> >> *Subject: *Re: RAM disks for cache? >> >> >> >> Yes, we have some similar servers in Production. We use ramdisks, it >> works fine. You could also theoretically give ATS a large memory cache and >> small disk (proxy.config.cache.ram_cache.size). But then that cache is >> shared across all remaps, and you lose the control of different volumes for >> different domains, and ATS just generally isn't really designed for that. >> We've found ramdisks to work better in practice. >> >> I will note, our servers like this also have poor CPUs. We thought this >> would be ok when we bought them, but it turns out you really kind of need >> decent CPU for things like SSL, and poor CPUs also tend to have poor PCI >> lanes, which are important. Our servers like this tend to cap out around >> 10Gbps, despite +20Gbps NICs. I don't know if yours are similar, but if >> your memory-poor servers are also CPU-poor, you might have the same >> bottlenecks. And that's not ATS' fault, it seems unlikely any other caching >> proxy could do better. >> >> >> >> >> >> On Wed, Apr 7, 2021 at 10:12 AM Nick Dunkin <[email protected]> >> wrote: >> >> Hi, >> >> >> >> I am being asked if Traffic Server can be efficiently run (or run at all) >> on a disk *poor*, memory *rich *server. The specifics are out of scope >> for this forum, but the short version is that I’m being asked to make use >> of some existing hardware. >> >> >> >> I was considering creating a RAM disk from the several hundred GB of >> available memory on these servers. >> >> >> >> Does anyone have any experience of running Traffic Server this way? >> >> >> >> Thanks, >> >> >> >> Nick >> >> >> >> *Nick Dunkin* >> >> Director, Software Engineering >> >> Manager – Architecture and New Product Introduction >> >> *o: * *+1 678.258.4071* >> >> *e:* [email protected] >> >> >> >> [image: [email protected]] >> >>
