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From NikolaiTom <nikolai.ronnin...@tomra.com>
Subject EnableJournalDiskSyncs slow on SAN - safe to disable?
Date Wed, 14 May 2014 14:44:14 GMT
We are running an ActiveMQ production environment, a Windows 2008 Server
running on a VMWare ESX host, stored on an EMC SAN. 

For all other purposes this system is quick and responsive, but the KahaDB
fsync call/EnableJournalDiskSync is a major problem for performance. 

With the default on setting we get about 3MB/sec, if we turn it off we get
300MB or above - a 100x increase. 

This is most likely related to the fsync call not returning before the data
has passed through the SSD cache on the SAN and stored on the RAID 6 disks. 

However, since we have an enterprise-grade SAN with SSD and battery backup,
connected to a UPS we're probably less likely to lose data than if we were
running on a normal server? If the data have reached the SAN SSD cache we
should be pretty safe? 

We've already researched using multiple KahaDB stores and spliting the
queues, but even that will most likely not give us the performance headroom
we need for growing the next 2-3 years. 

Any input on wether or not we could turn EnableJournalDiskSyncs off would be
greatly appreciated :) 

Thanks, 
Nikolai





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