1/18/2023 0 Comments Aws scsi disk map to xvd![]() ASM storage configurationĪSM does not use OS file systems or volume managers but has its own way of managing volumes and files. I don’t have hard numbers but a long time ago I was told it could be an overhead of up to 20%. Wrong alignment causes some reads and writes to be broken in 2 pieces causing extra IOPS. As MSDOS partitioning is limited to 2 TiB () it will probably be a thing of the past in a few years but for now we have to deal with it. If you use newer partition methods (GPT) then the issue is gone (but many BIOSes, boot methods and other tools cannot handle GPT). If you’re not using an Intel X86_64 based operating system then chances are you have no alignment issues at all (the only exception I know is Solaris if you use “fdisk”, similar problem). These days we have completely different physical disk geometries (and sometimes even different sector sizes, another interesting topic) but we still have the legacy of the old days. Because you need some header information for boot block and partition table, the smart guys back then thought it was a good idea to start the first block of the first data partition on track 1 (instead of track 0). The old partitioning scheme was invented when physical spinning rust was formatted with 63 sectors of 512 bytes per disk track each. ![]() The only thing you need to remember is that classic “MS-DOS” disk partitioning, by default, starts the first partition on the disk at the wrong offset (wrong in terms of optimal performance). I’ve written 2 blogposts on the matter of alignment so I am not going to repeat myself on the details. Should we use ASMlib or are there alternatives? If so, which ones and how to manage those?.What methods are available to set alignment correctly and to verify?.When do we have issues with disk alignment and why?.The questions could be summarized as follows: $Disk_ID = ( Get-Partition -DiskId $Path).Because of the many discussions and confusion around the topic of partitioning, disk alignment and it’s brother issue, ASM disk management, hereby an explanation on how to use UDEV, and as an extra, I present a tool that manages some of this stuff for you. Return $DriveLetter,$VirtualDevice,$PartitionNumber $PartitionNumber = (Get-Partition -DiskId $Path).PartitionNumber $DriveLetter = ((Get-Partition -DiskId $Path).AccessPaths).Split(",") $DriveLetter = (Get-Partition -DiskNumber $DiskNumber).DriveLetter $PartitionNumber = (Get-Partition -DriveLetter C).PartitionNumber $DiskNumber = (Get-Disk -Path $Path).Number $Device = ((Get-EC2Volume -VolumeId $EbsVolumeId ).Attachment).Device $EbsVolumeId = $SerialNumber.Substring(0,20).Replace("AWS","AWS-") $EbsVolumeId = $SerialNumber.Substring(0,20).Replace("vol","vol-") $SerialNumber = (Get-Disk -Path $Path).SerialNumber For more information, see Upgrade PV drivers on Windows instances. Your Windows AMI uses Red Hat PV drivers, you can update your instance to use the Citrixĭrivers. If you launch an instanceįrom a Windows AMI that uses AWS PV or Citrix PV drivers, you can use the relationshipsĭescribed on this page to map your Windows disks to your instance store and EBS volumes. ![]() ![]() Instance store and EBS volumes to Windows disks and drive letters. Windows Amazon Machine Images (AMIs) contain a set of drivers that are used by Amazon EC2 to map More information, see Device names on Windows instances. When you add a volume to your instance, you specify the device name that Amazon EC2 uses. For more information, see Make an Amazon EBS volume available for use on Instance, or attach them while your instance is running. You can also add EBS volumes when you create your AMI or launch your That are available to your instance, you must specify them when you create your AMI or Instance store volumes available to the instance. For more information, see Instance volume limits.ĭepending on the instance type of your instance, you'll have from 0 to 24 possible Windows instance uses AWS PV or Citrix PV drivers, you can optionally add up to 25 Your Windows instance comes with an EBS volume that serves as the root volume. ![]()
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