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do some errors more prone to SQL server on VMs?

Posted on 2014-07-22
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Last Modified: 2014-07-31
From your experience, have you seen some errors repeat more so in the virtual environment more than
 SQL servers hosted in physical boxes?
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Question by:25112
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by:25112
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for example, when we run the below, we get them only in the boxes that are virtual.. we have not seen this error in any of the physical servers so far:


EXEC master.dbo.xp_readerrorlog 0, 1, 'Error: 823'  
EXEC master.dbo.xp_readerrorlog 1, 1, 'Error: 823'
EXEC master.dbo.xp_readerrorlog 2, 1, 'Error: 823'
EXEC master.dbo.xp_readerrorlog 3, 1, 'Error: 823'
EXEC master.dbo.xp_readerrorlog 4, 1, 'Error: 823'
EXEC master.dbo.xp_readerrorlog 5, 1, 'Error: 823'
EXEC master.dbo.xp_readerrorlog 6, 1, 'Error: 823'
 
EXEC master.dbo.xp_readerrorlog 0, 1, 'Error: 824'  
EXEC master.dbo.xp_readerrorlog 1, 1, 'Error: 824'
EXEC master.dbo.xp_readerrorlog 2, 1, 'Error: 824'
EXEC master.dbo.xp_readerrorlog 3, 1, 'Error: 824'
EXEC master.dbo.xp_readerrorlog 4, 1, 'Error: 824'
EXEC master.dbo.xp_readerrorlog 5, 1, 'Error: 824'
EXEC master.dbo.xp_readerrorlog 6, 1, 'Error: 824'
 
 could you try this in your VM box vs physical box in non-peak hours to confirm/check/infer?
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by:Kelvin Sparks
Kelvin Sparks earned 125 total points
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I have tried this on both a physical server, and a vm - both work correctly.

Please note the following change

EXEC master.dbo.xp_readerrorlog 0, 1, N'Error: 823'  

Without the N (for nvarchar) it would not work in either.

Kelvin
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by:25112
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Kelvin

>>I have tried this on both a physical server, and a vm - both work correctly.
you mean you got zero entries back.. meaning no such errors at all? was it 2008?

>>Without the N (for nvarchar) it would not work in either.
It brings back records for me? I thought it won't work only if there are Unicode characters inside the quotes?
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Ryan McCauley earned 375 total points
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Any occurrence of those errors is a major concern, regardless of whether it's on a physical or virtual server. Both of those errors (823 and 824) are serious file consistency errors that indicate a massive concern at the storage layer (or at the OS layer as it communicates with storage). I'd immediately raise the issue with your OS and Storage Administrators (if that's not also you) to try and find the cause.

That said, there's nothing about a VM that would cause issues of any kind to occur more frequently than on a physical server - it should be transparent to the virtualized OS and applications, so they should be unaware of whether the host is physical or virtual. That said, virtualized environments have an additional layer of abstraction between the application and the hardware - instead of app -> OS -> hardware, it's app -> OS -> hypervisor -> hardware, which is an additional place that problems can arise. It will tend to exacerbate any latency or resource crowding issues you're already experiencing, so VMs tend to expose issues that already exist.

For these errors in particular, it's an indication that the VM can't save reliably to the shared storage. Since you don't see the issue on your physical servers, what's different about the VMs that would cause these storage issues to manifest? Some questions to ask:

 - Are other VMs on the server experiencing slow storage access times, or just the SQL Servers?
 - Are you using iSCSI or Fiber for your storage? iSCSI can be impaired by other network bandwidth issues, so check your switches - Fiber switches can also get crowded and lead to impairments, but they're significantly faster and tend to be dedicated to storage, but something to check.
 - Are all the VMs hosted by a single virtual host machine? If so, is there an issue with the HBA or storage access in that server?
 - Is the host machine(s) under these VMs crowded for resources, meaning the VMs can't get the resources they need in an acceptable amount of time?

I'd check the performance and resource load of the host underneath these VMs to see if it looks like there's a problem there. Though it could be related to the actual storage as well, but since you're only seeing it on the VMs and not the physical SQL Servers, I'd expect it's an issue present on the physical VM host machines rather than at the storage layer.
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by:25112
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thank u for the detailed response and help-guidance!
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