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Category: Storage

Retrieving Disk Block Size With Powershell

Published 2017-09-07 by Kevin Feasel

Naveen Kumar shows how to use Powershell to find out the block size of a particular disk in Windows:

Do you need to worry about disk block size?
I would suggest you to read below articles for getting better understanding on this topic

Disk Partition Alignment Best Practices for SQL Server
WHAT IS SQL SERVER’S IO BLOCK SIZE?

Post discussion, the next question was how do we check the disk block size for a given server?
You can do it from command line using FSutil utility. But let’s do it with PowerShell.

Read on for the code.

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Azure Archive Blob Storage

Published 2017-09-01 by Kevin Feasel

James Serra talks about a new tier of blob storage:

Last year Microsoft introduced Azure Cool Blob storage, which cost customers a penny per GB per month in some Azure regions.  Now, users have another, lower-cost option in Azure Archive Blob Storage, along with new Blob-Level Tiering data lifecycle management capabilities.  So there are now three Azure blog storage tiers: Hot, Cool, and Archive.

Azure Archive Blob Storage costs 0.18 cents per GB per month when the service is delivered through its cloud data center in the East US 2 (for comparison, in the same region hot is 1.8 cents and cool is 1.0 cents per GB per month) .  Customers can expect a 99 percent availability SLA (service level agreement) when the service makes its way out of the preview stage.

This is Azure’s response to AWS Glacier.  The immediate sticker price is a bit higher, but if there aren’t any incremental costs associated with deletion, uploading, or retrieving files, then it could end up matching Glacier in TCO.

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When CHECKDB Snapshots Run Out Of Disk Space

Published 2017-08-28 by Kevin Feasel

Andy Galbraith walks through an error message in DBCC CHECKDB when the snapshot runs out of disk space:

Looking in the SQL Error Log there were hundreds of these combinations in the minutes immediately preceding the job failure:

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The operating system returned error 665(The requested operation could not be completed due to a file system limitation) to SQL Server during a write at offset 0x000048a123e000 in file ‘E:\SQL_Data\VLDB01.mdf:MSSQL_DBCC17‘. Additional messages in the SQL Server error log and system event log may provide more detail. This is a severe system-level error condition that threatens database integrity and must be corrected immediately. Complete a full database consistency check (DBCC CHECKDB). This error can be caused by many factors; for more information, see SQL Server Books Online.

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Error: 17053, Severity: 16, State: 1.

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E:\SQL_Data\VLDB01.mdf:MSSQL_DBCC17: Operating system error 665(The requested operation could not be completed due to a file system limitation) encountered.

Read on for more information, including a rough idea of how much space the snapshot requires as well as a few workarounds and hints.

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Managing Drives On Linux

Published 2017-07-25 by Kevin Feasel

David Klee walks through some basics of Linux administration with respect to drives and mountpoints:

We see that all four of the drives show up in the list. Because of the nature of how I presented the disks to the VM, the bootable drives (sdd) show up at the end of the chain instead of the beginning, but that’s OK. It doesn’t change how the disks are bootable.

We are going to use the Logical Volume Manager (LVM) to manage the disks for us instead of using regular partitions. On Windows-based servers, Windows has the ability to expand partitions without incurring any downtime, and we want to have the same flexibility from a Linux standpoint. With elevated priviledges (for the rest of the commands), let’s scan the drives to look at what it sees.

Read the whole thing.

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TempDB In Azure IaaS

Published 2017-07-20 by Kevin Feasel

Jim Donahoe shows how to use the temporary SSD on an Azure VM for SQL Server’s tempdb:

Remember, this disk is as the title of this section says…TEMPORARY! Do NOT put ANYTHING on this drive you cannot afford to lose. Don’t say nobody warned you either, because the drive itself contains a nice little txt file warning you, here is the EXACT text:

WARNING : THIS IS A TEMPORARY DISK.

Any data stored on this drive is SUBJECT TO LOSS and THERE IS NO WAY TO RECOVER IT.

Please do not use this disk for storing any personal or application data.

It’s good to see what you need to do to get this working.  I’ve found it just to be easier to set up a permanent SSD, but if you’re on a tight budget, this can save you some cash.

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Docker Persistence: Multi-Level Mounting

Published 2017-07-06 by Kevin Feasel

Andrew Pruski gives us a third option for persisting SQL Server database files in Docker containers:

Last week in Part Two I went through how to create named volumes and map them to containers in order to persist data.

However, there is also another option available in the form of data volume containers.

The idea here is that create we a volume in a container and then mount that volume into another container. Confused? Yeah, me too but best to learn by doing so let’s run through how to use these things now.

Read through for the step-by-step description.

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Separating Data And Log Files

Published 2017-06-26 by Kevin Feasel

Brent Ozar looks at an old chestnut:

So it’s time for a quiz:

  1. If you put all of a SQL Server’s data files & logs on a single volume, how many failures will that server experience per year?
    • Bonus question: what kinds of data loss and downtime will each of those failure(s) have?
  2. If you split a SQL Server’s data files onto one volume, and log files onto another volume, how many failures will that server experience per year?
    • Bonus question: what kinds of data loss and downtime will each of those failures have?

Think carefully about the answers – or read the comments to see someone else’s homework, hahaha – before you move on.

With SANs, this advice is not even that good on the performance side—especially with modern SANs which don’t let you dedicate spindles.  It definitely doesn’t fly on the reliability side.

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S3 Versus HDFS For Spark Data Storage

Published 2017-06-02 by Kevin Feasel

Reynold Xin, Josh Rosen, and Kyle Pistor argue that you should use blob storage (S3, Azure Blob, etc.) instead of disk when building a cloud-based Spark cluster:

Based on our experience, S3’s availability has been fantastic. Only twice in the last six years have we experienced S3 downtime and we have never experienced data loss from S3.

Amazon claims 99.999999999% durability and 99.99% availability. Note that this is higher than the vast majority of organizations’ in-house services. The official SLA from Amazon can be found here: Service Level Agreement – Amazon Simple Storage Service (S3).

For HDFS, in contrast, it is difficult to estimate availability and durability. One could theoretically compute the two SLA attributes based on EC2’s mean time between failures (MTTF), plus upgrade and maintenance downtimes. In reality, those are difficult to quantify. Our understanding working with customers is that the majority of Hadoop clusters have availability lower than 99.9%, i.e. at least 9 hours of downtime per year.

It’s interesting how opinion has shifted; even a year ago, the recommendation would be different.

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Selecting Into A Filegroup

Published 2017-05-08 by Kevin Feasel

Denis Gobo points out a new feature in SQL Server 2017:

With the CTP2 build of SQL Server 2017, you now have the ability of doing a SELECT INTO operation into a specific filegroup.

The syntax looks like this

SELECT * INTO TableName ON FileGroup FROM SomeQuery

What is the use of this you might ask? Well maybe you have some ad-hoc queries where you save some data but you don’t want it sitting on your expensive SAN. Or maybe you populate staging tables on the fly and you want it to end up on a specific SSD because you need the speed of the SSD disk for these operations.

This might also be helpful in migrating tables to different storage.

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Re-Provisioning Volumes In Azure

Published 2017-05-01 by Kevin Feasel

Robert Bishop shows how to create data disks in Azure and attach them to VMs:

Recently a client found this article on “Best Practices for SQL Server in Azure Virtual Machines” and wanted to re-provision his volumes to adhere to them.

No my first thoughts was wait, I’m a DBA, not a System Admin that’s not my role! But thinking more about it I realized the client views this as a SQL Server issue and I am the SQL Server Consultant and that it is my job to remedy this problem.

Not being 100% confident in Azure, I spun up a VM SQL Server and attempted to add some volumes.  To my surprise, this was way too easy.

Click through for the steps.

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