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Bug 1314120

Summary: [RFE] Unify scrub into the client queue
Product: [Red Hat Storage] Red Hat Ceph Storage Reporter: Samuel Just <sjust>
Component: RADOSAssignee: Samuel Just <sjust>
Status: CLOSED ERRATA QA Contact: shylesh <shmohan>
Severity: medium Docs Contact: Bara Ancincova <bancinco>
Priority: unspecified    
Version: 2.0CC: amainkar, bengland, ceph-eng-bugs, dzafman, gmeno, hnallurv, kchai, nlevine, rsussman, sjust, yweinste
Target Milestone: rc   
Target Release: 2.0   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: Doc Type: Enhancement
Doc Text:
.Scrub operations are now in the client queue The scrub and trimming operations have been moved to the client operations queue to prioritize client I/O more accurately.
 Story Points: ---
Clone Of: Environment:
Last Closed: 2016-08-23 19:32:59 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 1322504    

Description Samuel Just 2016-03-03 00:15:26 UTC 
Description of problem:

Previously, snap trimming and scrub happened in a background thread pool meaning that scrub and snap trimming were scheduled vs client ops at the whim of the os scheduler.  Instead, move them into the same queue with lower priority so that the queue implementation can prioritize client IO directly while avoid starvation.

The main things to test are:
1) scrub throughput is adequate when cluster is not loaded

For this, populate a cluster to let's say 50% full of a mix of rbd and radosgw objects (make sure no single radosgw bucket gets unreasonably large).  Initiate a scrub, make sure the progress is reasonable (doesn't hang, comparable to hammer completion time).  Scrubbing a single pg on a 3 osd cluster is probably adequate.

2) client IO latency doesn't suffer too much (hopefully improves!) compared with hammer during a scrub (deep and shallow)

Populate the cluster as above.  Pick a few precreated rbd images and run fio small writes. Record 99th percentile latency and average throughput while scrubbing (you can probably just set the scrub interval to be very so that they are always scrubbing).  Verify that these do not suffer compared with hammer.
Comment 3 Neil Levine 2016-03-03 00:23:48 UTC 
Acking this for 2.0 but it needs a conversation with QE to confirm they feel this can be tested.
Comment 12 Ben England 2016-07-19 16:15:51 UTC 
not clear if Sam is talking about scrubbing, deep scrubbing or both?  Scrubbing just scans metadata right? which may just be cached for our small disk drives when large RBD objects are used.

-ben
Comment 14 errata-xmlrpc 2016-08-23 19:32:59 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2016:1755