Bob Duffy's Blobby Blog : Disks

Using a SAN to Initialize Replication

boduff — Sat, 16 May 2009 12:50:00 GMT

I've chatted to a few customers about the possibnility of using a SAN based snapshot to initialise transactional replication.

This can be fantastic when you are using a replica to provide "near real time" reporting. Up until now, documentation has been a bit light on the ground on this apporoach, and people have been cautious to try it. The results can really save a lot of time, such as getting a 17 TB replicated solution fully restored in a couple of hours!

My fellow MCM, Benjamin Wright-Jones in conjunction with the SQLCAT team has written a technical article based on his experience gettign this to work http://sqlcat.com/technicalnotes/archive/2009/05/04/initializing-a-transactional-replication-subscriber-from-an-array-based-snapshot.aspx

This gives step by step instructons on the procedure. Great stuff!

I think that in a short space of time anyone doing replication with a VLDB and SAN will consider this approach. Partly for technical reasons and party political. I mean you've just paid a fortune for that SAN - put it to work ;-)

Improving SQL Disk Performance #2 Windows Stripe Size

boduff — Sat, 26 Jan 2008 23:42:09 GMT

There are some urban legends around the Windows stripe size that you should set for SQL Server. I have seen recommendations of 64k for both data and log internally at Microsoft by some heavy hitting data Dudes, so that is good enough for me ;-)

Generally a Storage Area Network will have a 64k block size anyway - so I like to match the size of the windows stripe to the block size of the underlying disk subsystem.

How to Change the Windows Strip Size

This can only be selected when you format the disk. Also know as "Allocation Unit Size". beware as the default is only 4k.

One thing to be aware of is that NTFS compression is not supported with a block size of 64. But no one uses that with SQL Server - right !!

How to Query the Stripe Size?

fsutil fsinfo ntfsinfo F:

Sample output shows 4k windows format stripe size

NTFS Volume Serial Number : 0xe660d46a60d442cb
Number Sectors : 0x00000000010ea04f
Total Clusters : 0x000000000021d409
Free Clusters : 0x00000000000f222a
Total Reserved : 0x0000000000003550
Bytes Per Sector : 512
Bytes Per Cluster : 4096
Bytes Per FileRecord Segment : 1024
Clusters Per FileRecord Segment : 0
Mft Valid Data Length : 0x0000000003eab000
Mft Start Lcn : 0x0000000000000004
Mft2 Start Lcn : 0x000000000010ea04
Mft Zone Start : 0x0000000000003ea0
Mft Zone End : 0x0000000000004700

Improving SQL Disk Performance #1 Partition Alignment

boduff — Sat, 26 Jan 2008 23:31:56 GMT

There is a great article that you should read before configuring a disk subsystem for SQL Server. Predeployment I/O Best Practices.

As mentioned, one of the common pitfalls is not ensuring that the offset of the first block is "64k" or a multiple thereof.

Longhorn Server and Vista resolve this issue by using am offset of 1024. if you are using windows 2003 and this is incorrectly configured you could be loosing 40% plus of your disk i/o!

How to check partition offset (vbs script)

strComputer = "."
Set objWMIService = GetObject("winmgmts:\\" & strComputer & "\root\CIMV2") Set colItems = objWMIService.ExecQuery( _
"SELECT * FROM Win32_DiskPartition",,48)

For Each objItem in colItems

Wscript.Echo "Disk: " & objItem.DiskIndex & " Partition: " & objItem.Index & " StartingOffset: " & objItem.StartingOffset/1024 & "KB"

Wscript.Echo

you can also use diskpart -i

How to fix an incorrect offset:

If you have Windows 2003 SP1m the diskpart.exe command has an extra parameter /align that can be used to ensure that the partition is aligned. See http://technet2.microsoft.com/windowsserver/en/library/ca099518-dde5-4eac-a1f1-38eff6e3e5091033.mspx?mfr=true

The Humble Desktop Reaches a Terra

boduff — Wed, 16 May 2007 13:55:22 GMT

Hitachi have released a 1TB SATA II drive. What is more impressive than the size is the fact that according to Toms Hardware Guide it benchmarks as well as the famous Raptor drives. One of which I have lovingly in my development box at home, having replaced the SCSI system completely with SATA.

I'd be very interested to see how many IO's 4 of these striped give SQL Server. Could be an option for the budget conscious, or at the least for scratch space. Build your multi terrabyte storage for under 5k ;-)

I'm off to buy a few for Home Media Centre.

http://www.komplett.ie/k/ki.aspx?sku=335460

Flash - aha Saviour of the Database

boduff — Wed, 16 May 2007 13:44:40 GMT

A new wave of tecnology is about to hit enterpise SQL SAN's. The humble flash disk scaled up to 1TB. In theory this gives incredibiliy low IO latency and eliminates the descrepancies between random/sequential IO and slowness due to a disk filling up!

The RamSAN from Texas Memory Systems claims 1TB of Solid State Storage with 3.2 million IOPS! http://www.superssd.com/products/ramsan-400/

Expect High end SQL Server systems to use this for tempdb and high hitting areas like the ReportServerTemp database or ETL staging disks soon.

I can't wait so I'm tryin to get hold of this baby for my trusty Dell 820 laptop with 64 bit SQL Server on it. http://www.reghardware.co.uk/2007/04/03/transcend_touts_expresscard_disk/

These solid state disks are also great for increasing Windows Vista Performance with the new "Ready Boost" feature

http://www.microsoft.com/windows/products/windowsvista/features/details/readyboost.mspx