janipewter

Very slow write speed

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Hi all, currently on unraid trial with the view to purchasing two basic licences soon. I'm running two HP N40L microservers. I'm currently about 250GB of the way in to moving 7TB of data onto the first box and the write speed seems very poor.

 

All devices are connected with gigabit network and iperf confirms 925Mbit/sec speed between the unraid box and the one which is copying to it. There is only one drive in the unraid box so far, a brand new 4TB 5400RPM Seagate. I am not using parity as I do not need it, and the extra drive bay is more important to me.

 

I am using encrypted xfs filesystem and I realise the CPU in this box does not have AES-NI. I checked htop on the unraid console and the CPU is mainly hanging around 30-40% utilisation with some spikes up to 100% every few seconds. The file transfer is sustaining about 20MB/s. The box was previously running Ubuntu 16.04 without full disk encryption and could happily sustain 60MB/s+ write speed over the network.

 

Is the write speed due to unraid encrypting the files as it writes them, and my poor CPU without AES-NI? If so, will this affect the read performance at all?

 

Thanks.

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There obviously is some overhead when using encrypted volumes but there's also an overhead when writing many small files to any file system as opposed to fewer large files. Is the comparison you're making with Ubuntu fair in that respect? I would install a second disk and try copying the same files to an unencrypted volume to see if there's much difference.

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Hi, the files are all large, mostly 10GB+. I believe the comparison I have made is fair. I'm going to reformat this drive as xfs without encryption and see if the performance improves. Having full disk encryption is not imperative, I just thought it would be nice, but if it completely wipes out the write performance then I'd rather not bother with it. Will report back in a bit.

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I'll be interested to see the results of your test as I haven't seen any discussion about the computational cost of full disk encryption.

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Posted (edited)
22 hours ago, John_M said:

I'll be interested to see the results of your test as I haven't seen any discussion about the computational cost of full disk encryption.

 

OK, the overhead is not as much as I thought, I reformatted without full disk encryption and over the last 12 hours it has been sitting around 25-30MB/sec.

 

10 hours ago, johnnie.black said:

Check your bios, Microservers come with write cache disabled by default.

 

I've got the hacked BIOS on but write cache is turned off. Is it much of a performance gain to have it on? I'm not writing mission critical data to my arrays and both microservers are backed by a UPS anyway.

Edited by janipewter

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6 minutes ago, janipewter said:

Is it much of a performance gain to have it on?

Yes, max write speed with it disable on unRAID is around 25/30MB/s

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Got drive write caching enabled now, all seems fine and it happily sustains write speeds of 100MB/s over network.

 

Thanks all

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