Thanks Amos.
According to AWS docs:
> I/O size is capped at 256 KiB for SSD volumes
> When small I/O operations are physically contiguous, Amazon EBS attempts to merge them into a single I/O up to the maximum size. For example, for SSD volumes, a single 1,024 KiB I/O operation counts as 4 operations (1,024÷256=4), while 8 contiguous I/O operations at 32 KiB each count as 1operation (8×32=256). However, 8 random I/O operations at 32 KiB each count as 8 operations. Each I/O operation under 32 KiB counts as 1 operation.
So it's not so easy to figure out correlation between squid swap ops and AWS EBS ops. What I see from here is:
* Multiple squid swap in or swap out ops reading/writing contiguous blocks could be merged into one 256KB IO operation.
* Random squid operations could be handled as single 32KB IO operation.
On Thu, Jan 18, 2018 at 3:20 PM, Amos Jeffries <squid3@xxxxxxxxxxxxx> wrote:
On 19/01/18 12:04, Ivan Larionov wrote:
Thank you for the fast reply!
read_ops and write_ops is AWS EBS metric and in general it correlates with OS-level reads/s writes/s stats which iostat shows.
So if I understand you correctly max-swap-rate doesn't limit disk IOPS but limits squid swap ops instead and every squid operation could in theory use more than 1 disk IO operation. This means we can't really say "limit swap ops to 1500 because our disk can handle 1500 iops" but should figure out the number after testing different values.
Ok, I suppose I'll just do what Rock documentation says – will test different values and figure out what works for us.
If you know what the OS level IOP size is (eg usually 4KB) and the Squid rock IOP size Alex mentioned of 32KB. That should give you a number to divide the disk IOPS limit you want with to get a rough estimate for the appropriate Squid setting.
The tuning bit is just to see how much variance from that is caused by your traffic objects being different from the 32KB slot size.
Amos
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With best regards, Ivan Larionov.
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