Amazon Elastic Compute Cloud
User Guide for Linux Instances

Amazon EBS and NVMe

EBS volumes are exposed as NVMe block devices on Nitro-based instances. 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). The block device driver can assign NVMe device names in a different order than you specified for the volumes in the block device mapping.

Note

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

Some of these instance types also support NVMe instance store volumes. For more information, see NVMe SSD Volumes.

Identifying the EBS Device

EBS uses single-root I/O virtualization (SR-IOV) to provide volume attachments on Nitro-based instances using the NVMe specification. These devices rely on standard NVMe drivers on the operating system. These drivers typically discover attached devices by scanning the PCI bus during instance boot, and create device nodes based on the order in which the devices respond, not on how the devices are specified in the block device mapping. In Linux, NVMe device names follow the pattern /dev/nvme<x>n<y>, where <x> is the enumeration order, and, for EBS, <y> is 1. Occasionally, devices can respond to discovery in a different order in subsequent instance starts, which causes the device name to change.

We recommend that you use stable identifiers for your EBS volumes within your instance, such as one of the following:

  • For Nitro-based instances, the block device mappings that are specified in the Amazon EC2 console when you are attaching an EBS volume or during AttachVolume or RunInstances API calls are captured in the vendor-specific data field of the NVMe controller identification. With Amazon Linux AMIs later than version 2017.09.01, we provide a udev rule that reads this data and creates a symbolic link to the block-device mapping.

  • NVMe-attached EBS volumes have the EBS volume ID set as the serial number in the device identification.

  • When a device is formatted, a UUID is generated that persists for the life of the filesystem. A device label can be specified at the same time. For more information, see Making an Amazon EBS Volume Available for Use on Linux and Booting from the Wrong Volume.

Amazon Linux AMIs

With Amazon Linux AMI 2017.09.01 or later (including Amazon Linux 2), you can run the ebsnvme-id command as follows to map the NVMe device name to a volume ID and device name:

[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 package, nvme-cli, using the package management tools for your Linux distribution.

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):

[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.

[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:

[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.

I/O Operation Timeout

EBS volumes attached to Nitro-based instances use the default NVMe driver provided by the operating system. Most operating systems specify a timeout for I/O operations submitted to NVMe devices. The default timeout is 30 seconds and can be changed using the nvme_core.io_timeout boot parameter (or the nvme.io_timeout boot parameter for Linux kernels before version 4.6). For testing purposes, you can also dynamically update the timeout by writing to /sys/module/nvme_core/parameters/io_timeout using your preferred text editor. If I/O latency exceeds the value of this parameter, the Linux NVMe driver fails the I/O and return an error to the filesystem or application. Depending on the I/O operation, your filesystem or application can retry the error. In some cases, your filesystem may be remounted as read-only.

For an experience similar to EBS volumes attached to Xen instances, we recommend setting this timeout to the highest value possible. For current kernels, the maximum is 4294967295, while for earlier kernels the maximum is 255. The nvme.io_timeout boot parameter is already set to the maximum value for the following Linux distributions:

  • Amazon Linux AMI 2017.09.01 or later

  • Canonical 4.4.0-1041 or later

  • SLES 12 SP2 (4.4 kernel) or later

  • RHEL 7.5 (3.10.0-862 kernel) or later

You can verify the maximum value for your Linux distribution by writing a value higher than the suggested maximum to /sys/module/nvme_core/parameters/io_timeout and checking for the Numerical result out of range error when attempting to save the file.