Slow drive-to-drive transfer (ESXi)

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michaelmurfy

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#138871 20-Jan-2014 15:29

Hi all,

I'm having a bit of a problem with my Microserver running ESXi 5.5, when transferring from one drive to another it starts off at about 70MB/sec then goes right down to anywhere between 5MB/sec to 8MB/sec. I've replaced the drives, reinstalled ESXi and completely reinstalled Server 2012 on the main VM. It doesn't matter if the drives are thick or thin provisioned and the server has also got plenty of ram. Any ideas what may be causing the slow transfer speed?

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Zeon

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#970057 20-Jan-2014 15:44

Does your disk controller have write back mode enabled?

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michaelmurfy

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#970058 20-Jan-2014 15:46

Zeon: Does your disk controller have write back mode enabled?

Hmm this might be something I'll have to check. From memory this involves flashing a modified bios image to enable / disable.

Zeon

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#970064 20-Jan-2014 15:52

Are your disks just plugged into the motherboard's disk controller? Usually your RAID card would have an option and you would only turn it on with a battery backed unit. I believe this is because VMFS isn't like NTFS etc. where consecutive operations run fine on just normal disks - ie I think VMFS is more random hence the lower performance.

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gundar

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#970065 20-Jan-2014 15:53

Hi

I understand you have two virtual hard drives on a virtual Windows 2012 server and this all runs on ESXi. What is the physical drive configuration of the ESXi server - number of drives, type, controller?

Also, have you installed VMtools in the guest?

If you boot the server to a live Linux distribution, like Ubuntu, what is the output of testing tools, like hdparm as shown here: http://askubuntu.com/questions/87035/how-to-check-hard-disk-performance

michaelmurfy

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#970153 20-Jan-2014 17:18

gundar: Hi

I understand you have two virtual hard drives on a virtual Windows 2012 server and this all runs on ESXi. What is the physical drive configuration of the ESXi server - number of drives, type, controller?

Also, have you installed VMtools in the guest?

If you boot the server to a live Linux distribution, like Ubuntu, what is the output of testing tools, like hdparm as shown here: http://askubuntu.com/questions/87035/how-to-check-hard-disk-performance

I've tested drive performance outside of ESXi and it all works fine. I've got 1x 250gb drive, 1x 1tb drive and 1x 4tb drive plugged into the Microserver's motherboard direct. Nothing fancy like raids or anything. There's VMtools on the guests.

The controller is the one that is direct on the motherboard on the Microserver.

Zeon

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#970161 20-Jan-2014 17:29

Yea you need to read up about VMFS and lack of write back cache I think. It makes a HUGE difference and I think is really a requirement. Maybe you can pass the disk raw into your VM?

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michaelmurfy

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#970177 20-Jan-2014 17:54

Zeon: Yea you need to read up about VMFS and lack of write back cache I think. It makes a HUGE difference and I think is really a requirement. Maybe you can pass the disk raw into your VM?

By default the Microserver emulates IDE on the drives, I've flashed a modified BIOS and changed this. The embedded controller does support write caching but is not battery backed so possibly not the best thing to enable. It's strange though since I don't remember it ever being this bad.

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#970179 20-Jan-2014 17:59

Not the first time I've seen people complain about slow disk performance in 2012. Also make sure you don't have any fancy file system dedupe features enabled in your guest.

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Snowflake

#970310 20-Jan-2014 21:27

you're obviously extracting a RAR archive from "location A" to "location B". As part of the process, RAR uses a temporary location (typically the same folder as the archive) for the temporary extracted file(s). This typically means that you're doing disk read I/O's and disk write I/O's to the same volume in the first instance. If you have three disks/spindles, it can often speed it up if you can set the RAR temporary extraction path to the third disk.

whats the I/O like when you simply copy a file from disk to disk?