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Using and Creating Mount Points in SQL Server


Using and Creating Mount Points in SQL Server

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Perry Whittle
Perry Whittle
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Comments posted to this topic are about the item Using and Creating Mount Points in SQL Server

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"Ya can't make an omelette without breaking just a few eggs" ;-)
M&M
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Hi Perry,

Very nice to see your article. I will definetly try this out. Thank you for sharing your knowledge on these topics.

M&M
Rich Mechaber
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Thanks for an informative article Perry, but I'm left wondering what the benefit is to creating/using mount points is. For containing SQL system files, they seem like just another way to create a virtual disk/shortcut to space on an NTFS volume. Or am I missing something?

Rich
Perry Whittle
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rmechaber (11/10/2011)
For containing SQL system files, they seem like just another way to create a virtual disk/shortcut to space on an NTFS volume.

They may be used for system files, database files, log files, tempdb files and backup files. As the article explains, you only have 26 drive letters total available to the operating system. Mounts points allow you to have multiple instances with multiple disk resources without the drive letter constraints.

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CDA
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So, the one limitation, that I still see with mount points, is still doing any kind of logical detection of free-space.
Say I have a stub drive (drive letter) that's 500mb

xp_fixeddrives will ONLY see the stub drive freespace; it doesn't matter if I have mount points of 2 TB of space underneath it.
some vendor apps fail to install, saying there's not enough free space to complete installation based on this.

the only way I've figured out around this is to drop down into powershell and
gwmi win32_volume|where-object {$_.filesystem -match "ntfs"}|ft name,capacity,freespace



Anyone know of a way (or i'd like sql to have something built-in) to figure this out within TSQL?



L-P Larsson
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I have setup both our SQL test-environment and production environment, both are two node clusters.
I installed SQL Server first, and then mereley replaced the default installations folders with mount-point-folders via rename, xcopy /o <renamed-folder> <new-folder-with-default-name>

OS: WS 2008 R2 Enterprise
SQL 2008 R2 Standard

Some things I learned doing this are:

-there is a bug in Windows when setting permissions on the mounted folder - one has to do that first from disk management (right-click partition and set permissions). I had quite a lot of error messages doing that and it was impossible to just close the properties dialog by clicking Ok, I had to use Cancel. But afterwards the permissions are right if one checks.

-The amount of free space has to be checked for each "mount-point-folder" since the amount of free space in the root folder only show how much it is free of the root disk.

-When done and documented: Very nice to have one folder structure per sql instance and still have different write cache policies for data-folder, log-folder and temp-db-folder on each LUN that is used for mount point folder in the underlying storage system! Smile
k-335975
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Perry,

I usually monitor Avg. Disk sec/Read and Avg. Disk sec/Write to check disk activity, without mount points adding this counters in perfmon is not an issue. But with mount points, I just see the letter of mount point and not underlying disks in the instance list of above counters. I tried to find the id's of the disks under mount points, but not able to relate those id's with actual disks.

Any ideas?

Thanks!
SAinCA
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This may be a dumb question from a total mount-point novice...

The dialog boxes showed a max disk size of a smidge over 7GB. Where does that come from? Is it a limitation? What...? (As in, please elucidate 'cos I don't know enough to ask the "right" question...:-))

Thanks! Helpful article indeed on a topic I'd never heard of but had wondered for years how to get around the 23-user disk limitation.
Perry Whittle
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SAinCA (11/10/2011)
The dialog boxes showed a max disk size of a smidge over 7GB. Where does that come from? Is it a limitation? What...? (As in, please elucidate 'cos I don't know enough to ask the "right" question...:-))

Are you referring to the volume size of 7165MB shown in the wizard images? That is slightly under 7GB. The LUN sizes I used can be seen in the first image showing the Windows disk management console, there were a combination of 6GB and 7GB LUNs.

Remember the formatted size will always be less than the initial disk size presented!

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"Ya can't make an omelette without breaking just a few eggs" ;-)
Perry Whittle
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k-335975 (11/10/2011)
Perry,

I usually monitor Avg. Disk sec/Read and Avg. Disk sec/Write to check disk activity, without mount points adding this counters in perfmon is not an issue. But with mount points, I just see the letter of mount point and not underlying disks in the instance list of above counters. I tried to find the id's of the disks under mount points, but not able to relate those id's with actual disks.

Any ideas?

Thanks!

I do not have this information to hand at present. I will endeavour to provide this when I am back in blighty ;-)

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"Ya can't make an omelette without breaking just a few eggs" ;-)
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