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From Alan Carroll <>
Subject Re: Randomly high read rates
Date Tue, 17 Mar 2015 21:38:15 GMT
One thing to check for is (1) large objects in the cache and (2) multi-range requests. In this
case ATS will read the entire object and filter out that parts that aren't in the range requests.
The standard range acceleration only works for single range requests. Every object resides
on a single disk so if this is a specific object you would see this heavy read only on that
disk. There is a debug message for this but unfortunately it's "http_trans" which generates
*a lot* of output. If you're willing to do a minor tweak of the source, look in
for the line reading "Unable to accelerate range request" and change the tag from "http_trans"
to something more specific such as "http_trans_range" and then use that as the debug tag.
This may not be the problem, but it is worth taking a look.

     On Tuesday, March 17, 2015 4:12 PM, Tommy Lee <> wrote:

 Hi everybody,
   We are using ATS 4.2.1 with raw disks config and volume and hosting configs enabled. 
 And we're experiencing strange high read rates randomly at one disk.   We use LSI Megaraid
configured with RAID 0 ( Write back, Read Ahead, Cached IO and write cache, strip size 1MB
).   My question is: There is someway to see with debug tags what's is going on ?    
 ATS can be performing some maintenance tasks that randomly read disk at higher rates ?
   IOPs goes up to 450 and read speed reaches (90 MB/s) staying for 30~50 seconds and then
goes back to normal.
I would thank if anyone can give some direction where to search for this debug inside the

Best regards,

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