Re: Fwd: Re: Blocked ops after change from filestore on HDD to bluestore on SDD

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I am having quite a few openldap servers (slaves) running also, make 
sure to use proper caching that saves a lot of disk io.  




-----Original Message-----
Sent: 28 February 2019 13:56
To: uwe.sauter.de@xxxxxxxxx; Uwe Sauter; Ceph Users
Subject: *****SPAM***** Re:  Fwd: Re: Blocked ops after 
change from filestore on HDD to bluestore on SDD

"Advanced power loss protection" is in fact a performance feature, not a 
safety one.


28 февраля 2019 г. 13:03:51 GMT+03:00, Uwe Sauter 
<uwe.sauter.de@xxxxxxxxx> пишет:

	Hi all,
	
	thanks for your insights.
	
	Eneko,
	

		We tried to use a Samsung 840 Pro SSD as OSD some time ago and 
it was a no-go; it wasn't that performance was bad, it 
		just didn't work for the kind of use of OSD. Any HDD was 
better than it (the disk was healthy and have been used in a 
		software raid-1 for a pair of years).
		
		I suggest you check first that your Samsung 860 Pro disks work 
well for Ceph. Also, how is your host's RAM?


	As already mentioned the hosts each have 64GB RAM. Each host has 3 
SSDs for OSD usage. Each OSD is using about 1.3GB virtual
	memory / 400MB residual memory.
	
	
	
	Joachim,
	

		I can only recommend the use of enterprise SSDs. We've tested 
many consumer SSDs in the past, including your SSDs. Many 
		of them are not suitable for long-term use and some weard out 
within 6 months.


	Unfortunately I couldn't afford enterprise grade SSDs. But I 
suspect that my workload (about 20 VMs for our infrastructure, the
	most IO demanding is probably LDAP) is light enough that wearout 
won't be a problem.
	
	The issue I'm seeing then is probably related to direct IO if using 
bluestore. But with filestore, the file system cache probably
	hides the latency issues.
	
	
	Igor,
	

		AFAIR Samsung 860 Pro isn't for enterprise market, you 
shouldn't use consumer SSDs for Ceph.
		
		I had some experience with Samsung 960 Pro a while ago and it 
turned out that it handled fsync-ed writes very slowly 
		(comparing to the original/advertised performance). Which one 
can probably explain by the lack of power loss protection 
		for these drives. I suppose it's the same in your case.
		
		Here are a couple links on the topic:
		
		
https://www.percona.com/blog/2018/02/08/fsync-performance-storage-devices/
		
		
https://www.sebastien-han.fr/blog/2014/10/10/ceph-how-to-test-if-your-ssd-is-suitable-as-a-journal-device/


	Power loss protection wasn't a criteria for me as the cluster hosts 
are distributed in two buildings with separate battery backed
	UPSs. As mentioned above I suspect the main difference for my case 
between filestore and bluestore is file system cache vs. direct
	IO. Which means I will keep using filestore.
	
	Regards,
	
		Uwe
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--
With best regards,
Vitaliy Filippov


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