{"id":743,"date":"2010-02-28T09:40:00","date_gmt":"2010-02-28T09:40:00","guid":{"rendered":"\/blogs\/paul\/post\/Using-diskpart-to-check-disk-partition-alignment.aspx"},"modified":"2017-04-13T09:51:38","modified_gmt":"2017-04-13T16:51:38","slug":"using-diskpart-and-wmic-to-check-disk-partition-alignment","status":"publish","type":"post","link":"https:\/\/www.sqlskills.com\/blogs\/paul\/using-diskpart-and-wmic-to-check-disk-partition-alignment\/","title":{"rendered":"Using diskpart and wmic to check disk partition alignment"},"content":{"rendered":"

(Check out our Pluralsight online training course: SQL Server: Improving Storage\u00a0Subsystem Performance<\/a>.)\u00a0<\/em><\/span><\/p>\n

A while ago I blogged about disk partition alignment, and how the default alignment of 31.5Kb on Windows Server 2003 can lead to enormous I\/O performance problems (see <\/span>Are your disk partition offsets, RAID stripe sizes, and NTFS allocation units set correctly?<\/span><\/a>). We’ve been on-site with clients this week and that topic came up again. I thought it would be useful to do a quick blog post showing how to use the diskpart and <\/span>wmic<\/span>\u00a0tools. Google\u00a0them for lots of info from the Microsoft site – but be careful not to play around with any of the destructive options on productions systems. The options I’m using below will not alter the disks in any way.<\/span><\/p>\n

Note: This stuff applies to MBR disks, not GPT or dynamic disks. Although these require correct alignment too, I don’t have any information on how to do it for those disks. The SQLCAT team will be publishing some guidelines but has not yet done so, AFAIK. Check out the SQLCAT team whitepaper Disk Partition Alignment Best Practices for SQL Server<\/a> for full details on this topic.<\/span><\/p>\n

Bring up a command prompt and type diskpart. You’ll see something like:<\/span><\/p>\n

C:\\Users\\Administrator>diskpart<\/span><\/p>\n

Microsoft DiskPart version 6.0.6001
\nCopyright (C) 1999-2007 Microsoft Corporation.
\nOn computer: MONKEY<\/span><\/p>\n

DISKPART><\/span><\/p><\/blockquote>\n

Next you need to list the logical disks that Windows knows about. Type list disk<\/span>. You’ll see something like:<\/span><\/p>\n

DISKPART> list disk<\/span><\/p>\n

\u00a0 Disk ###\u00a0 Status\u00a0\u00a0\u00a0\u00a0\u00a0 Size\u00a0\u00a0\u00a0\u00a0 Free\u00a0\u00a0\u00a0\u00a0 Dyn\u00a0 Gpt
\n——–\u00a0 ———-\u00a0 ——-\u00a0 ——-\u00a0 —\u00a0 —
\nDisk 0\u00a0\u00a0\u00a0 Online\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 136 GB\u00a0 1434 MB
\nDisk 1\u00a0\u00a0\u00a0 Online\u00a0\u00a0\u00a0\u00a0\u00a0 1116 GB\u00a0\u00a0\u00a0\u00a0\u00a0 0 B
\nDisk 2\u00a0\u00a0\u00a0 Online\u00a0\u00a0\u00a0\u00a0\u00a0 2036 GB\u00a0\u00a0\u00a0\u00a0\u00a0 0 B<\/span><\/p>\n

DISKPART>\u00a0<\/span><\/p><\/blockquote>\n

Disks 1 and 2 are two RAID arrays I’m using right now for the performance benchmarking series<\/a> I’m doing. Notice that the numbers in the Free<\/span> column aren’t correct – not sure why not.\u00a0<\/span><\/p>\n

To see the partitions on a disk, you need to set the diskpart<\/span> focus to be that disk. Type select disk X<\/span>, where X is the disk you want to focus on. You’ll see something like:<\/span><\/p>\n

DISKPART> select disk 1<\/span><\/p>\n

Disk 1 is now the selected disk.<\/span><\/p>\n

DISKPART><\/span><\/p><\/blockquote>\n

And now you can list the partitions on the disk using list partition<\/span>. You’ll see something like:<\/span><\/p>\n

DISKPART> list partition<\/span><\/p>\n

\u00a0 Partition ###\u00a0 Type\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Size\u00a0\u00a0\u00a0\u00a0 Offset
\n————-\u00a0 —————-\u00a0 ——-\u00a0 ——-
\nPartition 1\u00a0\u00a0\u00a0 Primary\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 1116 GB\u00a0 1024 KB<\/span><\/p>\n

DISKPART><\/span><\/p><\/blockquote>\n

This is the output from one of my Windows Servr 2008 servers, where the default partition offset is 1MB – which doesn’t lead to perf issues.<\/span><\/p>\n

On another Windows XP system, I get the following output:<\/span><\/p>\n

DISKPART> select disk 0<\/span><\/p>\n

Disk 0 is now the selected disk.<\/span><\/p>\n

DISKPART> list partition<\/span><\/p>\n

\u00a0 Partition ###\u00a0 Type\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Size\u00a0\u00a0\u00a0\u00a0 Offset
\n————-\u00a0 —————-\u00a0 ——-\u00a0 ——-
\nPartition 1\u00a0\u00a0\u00a0 Primary\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 119 GB\u00a0\u00a0\u00a0 32 KB<\/span><\/p>\n

DISKPART><\/span><\/p><\/blockquote>\n

This disk isn’t aligned correctly. If this was a RAID array, I’d pay a perf penalty every time a read or write straddled a RAID stripe offset. See the blog post link at the top of this post for more details.<\/span><\/p>\n

Unfortunately, diskpart<\/span> isn’t always the best tool to use to get partition offsets, as it rounds up the values, and when there are multiple partitions, it can be hard to tell exactly what’s what, especially whtih lots of disks where you need to select each one and then list the partitions.<\/span><\/p>\n

In this case, use wmic<\/span> to get the exact numbers. The command is as follows:<\/span><\/p>\n

wmic partition get BlockSize, StartingOffset, Name, Index<\/span><\/p><\/blockquote>\n

For my server, I get the following output:<\/span><\/p>\n

BlockSize\u00a0 Index\u00a0 Name\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 StartingOffset
\n512\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0\u00a0\u00a0\u00a0 Disk #1, Partition #0\u00a0 1048576
\n512\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0\u00a0\u00a0\u00a0 Disk #2, Partition #0\u00a0 1048576
\n512\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0\u00a0\u00a0\u00a0\u00a0\u00a0 Disk #0, Partition #0\u00a0 1505755136<\/span><\/p><\/blockquote>\n

For dynamic disks, use:<\/span><\/p>\n

dmddiag.exe -v<\/span><\/p><\/blockquote>\n

Now – go out to your servers and check the partition alignment – fixing this can give you up to 30-40% I\/O performance boost!!<\/span><\/p>\n

How do you fix it? Well, that’s the downside – fixing it means reformatting the disk to have the correct partition offset or moving the data to a disk that already has the correct partition offset. Remember – although Windows Server 2008 creates disks with the correct offset,\u00a0taking a disk that was created on Windows Server 2003 and attaching it\u00a0to Windows Server 2008 will have no effect on the existing partition offset.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

(Check out our Pluralsight online training course: SQL Server: Improving Storage\u00a0Subsystem Performance.)\u00a0 A while ago I blogged about disk partition alignment, and how the default alignment of 31.5Kb on Windows Server 2003 can lead to enormous I\/O performance problems (see Are your disk partition offsets, RAID stripe sizes, and NTFS allocation units set correctly?). We’ve […]<\/p>\n","protected":false},"author":5,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[53,66,95],"tags":[],"class_list":["post-743","post","type-post","status-publish","format-standard","hentry","category-io-subsystems","category-performance-tuning","category-tools"],"yoast_head":"\nUsing diskpart and wmic to check disk partition alignment - Paul S. 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