A user runs the command “dd if=/dev/zero of=/dev/xvdfbs=1M” on a fresh blank EBS volume attached to a Linux instance.
Which of the below mentioned activities is the user performing with the command given above?
A.
Creating a file system on the EBS volume
B.
Mounting the device to the instance
C.
Pre warming the EBS volume
D.
Formatting the EBS volume
Explanation:
When the user creates a new EBS volume and is trying to access it for the first time it will encounter reduced IOPS due
to wiping or initiating of the block storage. To avoid this as well as achieve the best performance it is required to pre warm
the EBS volume. For a blank volume attached with a Linux OS, the “dd” command is used to write to all the blocks on
the device. In the command “dd if=/dev/zero of=/dev/xvdfbs=1M” the parameter “if =import file” should be set to one of
the Linux virtual devices, such as/dev/zero. The “of=output file” parameter should be set to the drive that the user wishes
to warm. The “bs” parameter sets the block size of the write operation; for optimal performance, this should be set to 1
MB.
C
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correct answer is D.
Formatting the EBS volume
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Formattind to what?
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The user is overwriting the volume/ secure erasing data, the source and destination are switched in the question
dd if= of= [Options]
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It called zeroing not formatting.
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Answer is : C
Reference : http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/disk-performance.html
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C.
There are two way to pre warm
“dd if=/dev/zero of=/dev/xvdf bs=1M” for new volume
“dd if=/dev/xvdf of=/dev/zero bs=1M” for restored EBS volume from snapshot
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C
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Quite confusing and I believe question is poorly worded or outdated?
This question is referring to EBS volume, rather than instance volume.
The command is relevant for instance storage rather than EBS volume.
For EBS Volume we should use dd or fio commands:
sudo dd if=/dev/xvdf of=/dev/null bs=1M
source: http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-initialize.html
anyhow, to pre-warm an EBS volume (which is only needed after if it was restored from snapshot, not for a newly created EBS), you need to READ from instead of WRITING to…
On Instance store – this is the opposite – you will need to WRITE to the disk to get better performance right at the beginning… and the command is:dd if=/dev/zero of=/dev/sdb bs=1M
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