ESXi 5.1 SSD guest write speed very slow

infira
infira used Ask the Experts™
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I have installed ESXi 5.1 on my server.
And machine has 4x vertex 256GB SSD drives, wich on drive is hot sphere. (RAID 5)
I have installed a Virtual Machine Windows7 for testing.

There i downloaded a AS SSD Benchmark for disk speed testing.
It says Seq 900MB/s for read, thats ok
But only 34.03 for Write, that is really slow. i Cant understand what seems to be the problem.



here some pictures for the result Speed Test resultVM settings screenshot VM SettingsVM performache graphfic VM performache graphfic
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Commented:
Try putting them in raid 10. No hot spare will be fine.

Raid 5 suffers write penalties, although I wouldn't have expected that much.

Author

Commented:
is there onther solution?, i cant remove Raid anymore
Most Valuable Expert 2015

Commented:
You are using desktop SSD's in a RAID array. Never do that. Those disks aren't built to work properly in an a RAID array. You will have to replace them with enterprise class SSD's (and make sure they are certified to work properly with your RAID controller, best practice is to buy them directly from your Server manufacturer, like Dell or HP). Or replace them with enterprise class standard disks.
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Author

Commented:
If i bought these SSD i previously read thad Vertex 4 works fine in Raid arrays
For example i use Raid 0 form my workstations, and i have very high speeds.
And it has worked veruy fine, no problems hasnt occured.

We have small busiess with up to 12 users into server, enterprise class SSD costs too much for us.
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017

Commented:
Those do seem slow! I would expect it's the RAID 5, or they do not work well in RAIDed.

here is a screenshot, from consumer SSDs in RAID 10 in ESXi 5.1, with a VM installed on the datastore!

SSD-RAID10
These are Kingston SSDs

and the following is using Enterprise Fusion-IO cards

SSD-FUSIONIO
DavidPresident
Top Expert 2010
Commented:
First, performance is awful because the RAID controller can't possibly keep up. You are seeing what happens when the controller cache gets full.  You are seeing how slowly uncached writes are.

So only way to fix that is go RAID1  (RAID10 will not be as efficient as RAID1

But better yet, use the vmdirect if you can and give the VM that needs SSDs 2 physical SSDs, and go software RAID1.   USe the HS to go 2 x RAID1s rather than a 3-disk RAID5 + 1.  Better 2 x RAID1s than a single RAID10 unless you have a file that is to large to fit on a single RAID1.

Author

Commented:
@hanccocka what card you using?
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017

Commented:
Fusion-IO ioDrives

http://www.fusionio.com/products/iodrive/

the original, MkI, replaced by the ioDrive2

http://www.fusionio.com/products/iodrive2/

Why the need for all the speed?

(unless you are doing VDI)

Author

Commented:
i dont need speed that much, but 30 mb is pretty slow, even my museum old HDD performed better
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017

Commented:
If you are comparing physical with virtual machines, virtual computers will always be slower, by nature of the I/O which is virtualised, that's the trade off, compared to a physical computer.

Its it impacting performance to the end user.

Author

Commented:
that i know, but the performance slowlyness should'nt be that high
Write speed should be around 400-500MB not 30
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017

Commented:
Never seen the write speed at 400-500MB, you can see my example at RAID 10.

Author

Commented:
Ok, maybe i exaggerate, but i think the 30MB/s is low.
For conclusion you said, my raid configuration is wrong?
VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017
Commented:
RAID 1, and RAID 10 will give you better performance.

Author

Commented:
For now i accept your solution, ill try it later, now i must copy data back to old server. And try Raid 10 or 1
DavidPresident
Top Expert 2010

Commented:
30MB is not low for a RAID5 doing nearly full uncached random I/O.  SSDs are purchased for low latency, not throughput.

Author

Commented:
@dlethe you claim that 30MB is normal in raid 5? considering tha singel drive should perfrom ~510MB seq write speed
DavidPresident
Top Expert 2010

Commented:
No, I claim that 30MB is normal in YOUR specific situation (random I/O, non-cached, RAID5, grossly mismatched I/O size).  

How the single drive performs on sequential writes would only be relevant if you were benching sequential writes.  You aren't. No such thing as a sequential write when it comes to what HDDs/SDDs do behind a RAID5 controller.  Then factor real world likelihood that your I/O is random and uncached, and you'll understand why.

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