yes SSD-Journal helps a lot (if you use the right SSDs)
What SSDs to avoid for journaling from your experience? Why?
>
> We're seeing very disappointing Ceph performance. We have 10GigE
> interconnect (as a shared public/internal network).
Which kind of CPU do you use for the OSD-hosts?
Intel(R) Xeon(R) CPU E5-2660 v2 @ 2.20GHz
FYI, we are hosting VMs on our OSD nodes, but the VMs use very small amounts of CPUs and RAM
>
> We're wondering whether it makes sense to buy SSDs and put journals on
> them. But we're looking for a way to verify that this will actually
> help BEFORE we splash cash on SSDs.
I can recommend the Intel DC S3700 SSD for journaling! In the beginning
I started with different much cheaper models, but this was the wrong
decision.
What, apart from the price, made the difference? sustained read/write bandwidth? IOPS?
We're considering this one (PCI-e SSD). What do you think?
PX-128M6e-BK
Also, we're thinking about sharing one SSD between two OSDs. Any reason why this would be a bad idea?
> We're using Ceph for OpenStack storage (kvm). Enabling RBD cache
> didn't really help all that much.
The read speed can be optimized with an bigger read ahead cache inside
the VM, like:
echo 4096 > /sys/block/vda/queue/read_ahead_kb
Thanks, we will try that.
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