[squid-users] rock storage and max-swap-rate

[Ivan Larionov]

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 at treenet.co.nz> 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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