Slow diskperfomance in virtual guest

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Daniel Jonasson

New Member
Feb 22, 2019
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Hi!

I have configured a Dell Poweredge T20 with a Xeon proccessor, 24 GB ECC memory .
I have four 256 GB SSD connected to a raid 10 with raid controller LSI SAS 9211-8.
Four 2 TB HDD in raid 5 within Intel raidcontroller (integrated) as storage volume.
OS = Server 2019 Datacenter running HyperV. Installed on the SSD-volume.

Speeds of copying/transfering files are above 100 MB/sec within the host regardless of transfering files on the SSD volume or storage volume. However when making a virtual machine (also Server 2019) speeds are limited to about 10 MB/sec on the storage volume and 70 MB/sec on the SSD volume.
Doing the same thing directly on the host, tranfering files are about 300 MB/sec in the SSD volume and 80 MB/sec on the storage volume.
It can´t be network related since when I´m copying files within the guest/virtual machine the speeds are the same.
Why is the host so slow on writing to disk? Reading is far faster.
 

SIlviu

Member
May 27, 2016
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Where did you fit all those drives in that T20 ? What model are the SSD`s and HDD`s ? Datacenter on a T20 ?
 

Daniel Jonasson

New Member
Feb 22, 2019
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Where did you fit all those drives in that T20 ? What model are the SSD`s and HDD`s ? Datacenter on a T20 ?
There is 4 S-ata connectors on the motherboard which I use för the HDD´s. Also got a raid controller, LSI SAS 9211-8i, that supports up to eight more disks. For now I have 4 SSD connected.
The HDD´s are three Hitachi (HDS722020ALA330) and one Seagate barracuda ST2000DM006-2DM164.
Yes, datacenter edition due to license limit to only two virtual machines in server standard.
 

SIlviu

Member
May 27, 2016
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That first 2GB/s transfer got into RAM and then it slowly goes in D: ...
Do a crystaldiskmark on D: / RAID5 on a 2GB file and check writes

And standard edition is not limited to only 2 VM`s it only gives you 2 FREE Windows Server VM`s
 

Daniel Jonasson

New Member
Feb 22, 2019
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Thanks!
True about licensing.
I´m doing crystaldiskmark on the host at the moment. When finished I´ll make one on the guest as well. I´ll be back with results.
 

Daniel Jonasson

New Member
Feb 22, 2019
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Pretty equal results on the host and on the guest. So thoose fast tranfers on the host was due to RAM?
Should I consider raid 10 instead? I have tried enable and disable write cache without any major change in speed.
 

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SIlviu

Member
May 27, 2016
83
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Yes, that was the RAM, if you check resource monitor you will see a ram increase usage and 100% disk usage on D: even after it shows the transfer is complete, it will copy in background from ram.
If you want parity raid you need a good controller with cache and BBU. For what you have you should go Raid 10.
You did not tell what model are the SSD`s.
 

Daniel Jonasson

New Member
Feb 22, 2019
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Thanks!
Samsung MZ-7PD2560/0H7 is the SSD´s.
Maybee I have to reconfigure. Doing raid 10 with 2 TB disks would not last so long. Pherhaps I´ll wait untill I can put my hands on a couple of 8 TB or more.
I was looking at running Unraid instead but since I´m running HyperV on my other server, hyperV would be easier. Pherhaps doing some Live Migration. This server will mostly serve movies so the data is not that critical. Read/write performance and amount of TB storage are priotorized.
 
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SIlviu

Member
May 27, 2016
83
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I have bad experience with samsung consumer ssd`s in raid, a lot of errors and very slow write after 4-5 months. If you want ssd`s in RAID go with Intel DC S4510.
Live Migration only works if the servers are in a domain.