Oracle Cloud Infrastructure Documentation

Protecting Data on NVMe Devices

Some instance shapes in Oracle Cloud Infrastructure include locally attached NVMe devices. These devices provide extremely low latency, high performance block storage that is ideal for big data, OLTP, and any other workload that can benefit from high-performance block storage.

Note that these devices are not protected in any way; they are individual devices locally installed on your instance. Oracle Cloud Infrastructure does not take images, back up, or use RAID or any other methods to protect the data on NVMe devices. It is your responsibility to protect and manage the durability the data on these devices.

Oracle Cloud Infrastructure offers high-performance remote block (iSCSI) LUNs that are redundant and can be backed up using an API call. See Overview of Block Volume for more information.

See Compute Shapesf for information about which instance types support local NVMe storage.

Finding the NVMe devices on your instance

You can identify the NVMe devices by using the lsblk command. The response returns a list. NVMe devices begin with "nvme", as shown in the following example for a BM.DenseIO1.36 instance:

[opc@somehost ~]$ lsblk
NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda       8:0    0 46.6G  0 disk
├─sda1    8:1    0  512M  0 part /boot/efi
├─sda2    8:2    0    8G  0 part [SWAP]
└─sda3    8:3    0   38G  0 part /
nvme0n1 259:6    0  2.9T  0 disk
nvme1n1 259:8    0  2.9T  0 disk
nvme2n1 259:0    0  2.9T  0 disk
nvme3n1 259:1    0  2.9T  0 disk
nvme4n1 259:7    0  2.9T  0 disk
nvme5n1 259:4    0  2.9T  0 disk
nvme6n1 259:5    0  2.9T  0 disk
nvme7n1 259:2    0  2.9T  0 disk
nvme8n1 259:3    0  2.9T  0 disk
[opc@somehost ~]$

Failure Modes and How to Protect Against Them

There are three primary failure modes you should plan for:

Protecting against the failure of an NVMe device

A protected RAID array is the most recommended way to protect against an NVMe device failure. There are three RAID levels that can be used for the majority of workloads:

  • RAID 1: An exact copy (or mirror) of a set of data on two or more disks; a classic RAID 1 mirrored pair contains two disks, as shown:
  • This image shows a RAID 1 array.

  • RAID 10: Stripes data across multiple mirrored pairs. As long as one disk in each mirrored pair is functional, data can be retrieved, as shown:
  • This image shows a RAID 10 array, with blocks mirrored and striped.

  • RAID 6: Block-level striping with two parity blocks distributed across all member disks, as shown.
  • This image shows a Raid 6 array.

For more information about RAID and RAID levels, see RAID.

Because the appropriate RAID level is a function of the number of available drives, the number of individual LUNs needed, the amount of space needed, and the performance requirements, there isn't one correct choice. You must understand your workload and design accordingly.

Options for Using a BM.DenseIO1.36 Shape

There are several options for BM.DenseIO1.36 instances with nine NVMe devices:

Create a single RAID 6 device across all nine devices. This array is redundant, performs well, will survive the failure of any two devices, and will be exposed as a single LUN with about 23.8TB of usable space.

Use the following commands to create a single RAID 6 device across all nine devices:

$ sudo yum install mdadm -y
$ sudo mdadm --create /dev/md0 --raid-devices=9 --level=6 /dev/nvme0n1 /dev/nvme1n1 /dev/nvme2n1 /dev/nvme3n1 /dev/nvme4n1 /dev/nvme5n1 /dev/nvme6n1 /dev/nvme7n1 /dev/nvme8n1
$ sudo mdadm --detail --scan | sudo tee -a /etc/mdadm.conf >> /dev/null

Create a four device RAID 10 and a five device RAID 6 array. These arrays would be exposed as two different LUNs to your applications. This is a recommended choice when you need to isolate one type of I/O from another, such as log and data files. In this example, your RAID 10 array would have about 6.4TB of usable space and the RAID 6 array would have about 9.6TB of usable space.

Use the following commands to create a four-device RAID 10 and a five-device RAID 6 array:

$ sudo yum install mdadm -y
$ sudo mdadm --create /dev/md0 --raid-devices=4 --level=10 /dev/nvme5n1 /dev/nvme6n1 /dev/nvme7n1 /dev/nvme8n1
$ sudo mdadm --create /dev/md1 --raid-devices=5 --level=6 /dev/nvme0n1 /dev/nvme1n1 /dev/nvme2n1 /dev/nvme3n1 /dev/nvme4n1
$ sudo mdadm --detail --scan | sudo tee -a /etc/mdadm.conf >> /dev/null

If you need the best possible performance and can sacrifice some of your available space, then an eight-device RAID 10 array is an option. Because RAID 10 requires an even number of devices, the ninth device is left out of the array and serves as a hot spare in case another device fails. This creates a single LUN with about 12.8 TB of usable space.

Use the following commands to create an eight-device RAID 10 array:

$ sudo yum install mdadm -y
$ sudo mdadm --create /dev/md0 --raid-devices=8 --level=10 /dev/nvme0n1 /dev/nvme1n1 /dev/nvme2n1 /dev/nvme3n1 /dev/nvme4n1 /dev/nvme5n1 /dev/nvme6n1 /dev/nvme7n1

The following command adds /dev/nvme8n as a hot spare for the /dev/md0 array:

$ sudo mdadm /dev/md0 --add /dev/nvme8n1    
$ sudo mdadm --detail --scan | sudo tee -a /etc/mdadm.conf >> /dev/null

For the best possible performance and I/O isolation across LUNs, create two four-device RAID 10 arrays. Because RAID 10 requires an even number of devices, the ninth device is left out of the arrays and serves as a global hot spare in case another device in either array fails. This creates two LUNS, each with about 6.4 TB of usable space.

Use the following commands to create two four-device RAID 10 arrays with a global hot spare:

$ sudo yum install mdadm -y
$ sudo mdadm --create /dev/md0 --raid-devices=4 --level=10 /dev/nvme4n1 /dev/nvme5n1 /dev/nvme6n1 /dev/nvme7n1
$ sudo mdadm --create /dev/md1 --raid-devices=4 --level=10 /dev/nvme0n1 /dev/nvme1n1 /dev/nvme2n1 /dev/nvme3n1

Creating a global hot spare requires the following two steps:

  1. Add the spare to either array (it does not matter which one) by running these commands:

    $ sudo mdadm /dev/md0 --add /dev/nvme8n1
    $ sudo mdadm --detail --scan | sudo tee -a /etc/mdadm.conf >> /dev/null
  2. Edit /etc/mdadm to put both arrays in the same spare-group. Add spare-group=global to the end of the line that starts with ARRAY, as follows:

    $ sudo vi /etc/mdadm.conf
    ARRAY /dev/md0 metadata=1.2 spares=1 name=mdadm.localdomain:0 UUID=43f93ce6:4a19d07b:51762f1b:250e2327 spare-group=global
    ARRAY /dev/md1 metadata=1.2 name=mdadm.localdomain:1 UUID=7521e51a:83999f00:99459a19:0c836693 spare-group=global

Monitoring Your Array

It's important for you to be notified if a device in one of your arrays fails. Mdadm has built-in tools that can be utilized for monitoring, and there are two options you can use:

  • Set the MAILADDR option in /etc/mdadm.conf and then run the mdadm monitor as a daemon
  • Run an external script when mdadm detects a failure

Set the MAILADDR option in /etc/mdadm.conf and run the mdadm monitor as a daemon

The simplest method is to set the MAILADDR option in /etc/mdadm.conf, and then run the mdadm monitor as a daemon, as follows:

  1. The DEVICE partitions line is required for MAILADDR to work; if it is missing, you must add it, as follows:

    $ sudo vi /etc/mdadm.conf
    DEVICE partitions     
    ARRAY /dev/md0 level=raid1 UUID=1b70e34a:2930b5a6:016we78d:eese14532
    MAILADDR <my.name@oracle.com>
  2. Run the monitor using the following command:

    $ sudo nohup mdadm –-monitor –-scan –-daemonize &
  3. To verify that the monitor runs at startup, run the following commands:

    $ sudo chmod +x /etc/rc.d/rc.local
    $ sudo vi /etc/rc.local

    Add the following line to the end of /etc/rc.local:

    nohup mdadm –-monitor –-scan –-daemonize &
  4. To verify that the email and monitor are both working run the following command:

    $ sudo mdadm --monitor --scan --test -1

    Note that these emails will likely be marked as spam. The PROGRAM option, described later in this topic, allows for more sophisticated alerting and messaging.

Run an external script when a failure is detected

A more advanced option is to create an external script that would run if the mdadm monitor detects a failure. You would integrate this type of script with your existing monitoring solution. The following is an example of this type of script:

$ sudo vi /etc/mdadm.events
  
#!/bin/bash
event=$1
device=$2
if [ $event == "Fail" ]
then
  <"do something">
else
 if [ $event == "FailSpare" ]
 then
  <"do something else">
 else
  if [ $event == "DegradedArray" ]
  then
   <"do something else else">
  else
   if [ $event == "TestMessage" ]
    then
    <"do something else else else">
   fi
  fi
 fi
fi
  
$ sudo chmod +x /etc/mdadm.events

Next, add the PROGRAM option to /etc/mdadm.conf, as shown in the following example:

  1. The DEVICE partitions line is required for MAILADDR to work; if it is missing, you must add it, as follows:

    $ sudo vi /etc/mdadm.conf
    DEVICE partitions     
    ARRAY /dev/md0 level=raid1 UUID=1b70e34a:2930b5a6:016we78d:eese14532
    MAILADDR <my.name@oracle.com>
    PROGRAM /etc/mdadm.events
  2. Run the monitor using the following command:

    $ sudo nohup mdadm –-monitor –-scan –-daemonize &
  3. To verify that the monitor runs at startup, run the following commands:

    $ sudo chmod +x /etc/rc.d/rc.local
    $ sudo vi /etc/rc.local

    Add the following line to the end of /etc/rc.local:

    nohup mdadm –-monitor –-scan –-daemonize &
  4. To verify that the email and monitor are both working run the following command:

    $ sudo mdadm --monitor --scan --test -1

    Note that these emails will likely be marked as spam. The PROGRAM option, described later in this topic, allows for more sophisticated alerting and messaging.

Simulate the failure of a device

You can use mdadm to manually cause a failure of a device to see whether your RAID array can survive the failure, as well as test the alerts you have set up.

  1. Mark a device in the array as failed by running the following command:

    $ sudo mdadm /dev/md0 --fail /dev/nvme0n1
  2. Recover the device or your array might not be protected. Use the following command:

    $ sudo mdadm /dev/md0 --add /dev/nvme0n1

    Your array will automatically rebuild in order to use the "new" device. Performance will be decreased during this process.

  3. You can monitor the rebuild status by running the following command:

    $ sudo mdadm --detail /dev/md0

What To Do When an NVMe Device Fails

Compute resources in the cloud are designed to be temporary and fungible. If an NVMe device fails while the instance is in service, you should start another instance with the same amount of storage or more, and then copy the data onto the new instance, replacing the old instance. There are multiple toolsets for copying large amounts of data, with rsync being the most popular. Since the connectivity between instances is a full 10Gb/sec, copying data should be quick. Remember that with a failed device, your array may no longer be protected, so you should copy the data off of the impacted instance as quickly as possible.

Using the Linux Logical Volume Manager

The Linux Logical Volume Manager (LVM) provides a rich set of features for managing volumes. If you need these features, we strongly recommend that you use mdadm as described in preceding sections of this topic to create the RAID arrays, and then use LVM's pvcreate, vgcreate, and lvcreate commands to create volumes on the mdadm LUNs. You should not use LVM directly against your NVMe devices.

Protecting Against the Loss of the Instance or Availability Domain

Once your data is protected against the loss of a NVMe device, you need to protect it against the loss of an instance or the loss of the availability domain. This type of protection is typically done by replicating your data to another availability domain or backing up your data to another location. The method you choose depends on your objectives. For details, see Recovery Time Objective (RTO) and Recovery Point Objective (RPO).

Replication

Replicating your data from one instance in one availability domain to another has the lowest RTO and RPO at a significantly higher cost than backups; for every instance in one availability domain, you must have another instance in a different availability domain.

For Oracle database workloads, you should use the built-in Oracle Data Guard functionality to replicate your databases. Oracle Cloud Infrastructure availability domains are each close enough to each other to support high performance, synchronous replication. Asynchronous replication is also an option.

For general-purpose block replication, DRBD is the recommended option. You can configure DRBD to replicate, synchronously or asynchronously, every write in one availability domain to another availability domain.

Backups

Traditional backups are another way to protect data. All commercial backup products are fully supported on Oracle Cloud Infrastructure. If you use backups, the RTO and RPO are significantly higher than using replication because you must recreate the compute resources that failed and then restore the most recent backup. Costs are significantly lower because you don't need to maintain a second instance. Do not store your backups in the same availability domain as their original instance.

Protecting Against Data Corruption or Loss from Application or User Error

The two recommended ways of protecting against data corruption or loss from application or user error are regularly taking snapshots or creating backups.

Snapshots

The two easiest ways to maintain snapshots are to either use a file system that supports snapshots, such as ZFS, or use LVM to create and manage the snapshots. Because of the way LVM has implemented copy-on-write (COW), performance may significantly decrease when a snapshot is taken using LVM.

Backups

All commercial backup products are fully supported on Oracle Cloud Infrastructure. Make sure that your backups are not stored in the same availability domain as their original instance.