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Amazon Elastic Compute Cloud
User Guide for Linux Instances

Amazon EBS and NVMe

With C5 instances, EBS volumes are exposed as NVMe block devices. The device names are /dev/nvme0n1, /dev/nvme1n1, and so on. The device names that you specify in a block device mapping are renamed using NVMe device names (/dev/nvme[0-26]n1).

Note

The EBS performance guarantees stated in Amazon_EBS_Product_Details are valid regardless of the block-device interface.

Identifying the EBS Device

Amazon Linux AMIs

With Amazon Linux AMI 2017.09.01 or later, you can run the ebsnvme-id command as follows to map the NVMe device name to a volume ID and device name.

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[ec2-user ~]$ sudo /sbin/ebsnvme-id /dev/nvme1n1 Volume ID: vol-01324f611e2463981 /dev/sdf

Amazon Linux also creates a symbolic link from the device name in the block device mapping (for example, /dev/sdf), to the NVMe device name.

Other Linux AMIs

With a kernel version of 4.2 or later, you can run the nvme id-ctrl command as follows to map an NVMe device to a volume ID. First, install the NVMe command line:

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[ec2-user ~]$ sudo yum install nvme

The following example gets the volume ID and device name. The device name is available through the NVMe controller vendor specific extension (bytes 384:4095 of the controller identification).

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[ec2-user ~]$ sudo nvme id-ctrl -v /dev/nvme1n1 NVME Identify Controller: vid : 0x1d0f ssvid : 0x1d0f sn : vol01234567890abcdef mn : Amazon Elastic Block Store ... 0000: 2f 64 65 76 2f 73 64 6a 20 20 20 20 20 20 20 20 "/dev/sdf..."

The lsblk command lists available devices and their mount points (if applicable). This helps you determine the correct device name to use. In this example, /dev/nvme0n1p1 is mounted as the root device and /dev/nvme1n1 is attached but not mounted.

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[ec2-user ~]$ lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT nvme1n1 259:3 0 100G 0 disk nvme0n1 259:0 0 8G 0 disk nvme0n1p1 259:1 0 8G 0 part / nvme0n1p128 259:2 0 1M 0 part

Working with NVMe EBS Volumes

If you are using Linux kernel 4.2 or later, any change you make to the volume size of an NVMe EBS volume is automatically reflected in the instance. For older Linux kernels, you might need to detach and attach the EBS volume or reboot the instance for the size change to be reflected. With Linux kernel 3.19 or later, you can use the hdparm command as follows to force a rescan of the NVMe device:

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[ec2-user ~]$ sudo hdparm -z /dev/nvme1n1

Before you detach an NVMe EBS volume, you should sync and unmount it. When you detach an NVMe EBS volume, the force option is implicitly enabled. Therefore, the instance does not have an opportunity to flush file system caches or metadata before detaching the volume.

Note

If you are using st1 or sc1 volumes, we recommend that you continue to use C4 instances for now. C5 currently does not support st1 or sc1 volumes.

I/O Operation Timeout

NVMe EBS volumes utilize the default NVMe driver in the operating system. Most operating systems have a timeout for I/O operations submitted to NVMe devices. The default timeout is 30 seconds and the maximum is 255 seconds.

On Linux systems, we recommend that you increase the timeout to 255 seconds using the nvme_core.io_timeout boot parameter. If you are using a current Amazon Linux AMI, we have already increased the default timeout for you.

With Linux kernel 4.14 and later, you can also configure the number of times that I/O operations can be retried. The default is 5 retries. You can configure a different value using the nvme_core.nvme_max_retries kernel boot parameter or at runtime using the following command:

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[ec2-user ~]$ echo 10 > /sys/module/nvme_core/parameters/max_retries