![]() ![]() Mdraid was used to create RAID0 arrays with a chunk size of 256k, for example: mdadm -create -verbose /dev/md0 -level=0 -c256 -raid-devices=2 /dev/sdi1 /dev/sdi2īlockdev is used to set the read-ahead buffer to 64k: blockdev -setra 65536 /dev/md0 Testing was done using bonnie++ on fast mode (-f flag, skips per-char tests). All instances were created in the us-east-1b Availability Zone and all EBS volumes attached were newly created specifically for this test. I created 5 c1.xlarge instances with 5 configurations: 4圎phemeral RAID0 local disk, single EBS, 2圎BS RAID0, 4圎BS RAID0, 8圎BS RAID0. 5ms to 10ms+įor this testing, c1.xlarge instances were used due to their high CPU performance, memory capacity, "I/O Performance: High" (according to Amazon), and 4 available 450GB ephemeral disks. Extremely variable performance - seek times can range from.Portable - an EBS volume can be connected to any instance in a single availability zone."Highly available" - AWS claims to provide redundancy and a lower failure rate than physical disks.Average random seek performance (6-7ms seek times per spindle).Ephemeral - if the instance shuts down, all data is lost. ![]() ![]() Abundant storage (up to 1.7TB on a c1.xlarge).Stable, predictable performance on par with a standard physical hard disk.Free (included in cost of EC2 instance).There are clear performance implications in choosing how to configure an EC2 instance’s disk subsystem, so I recently benchmarked some various ephemeral and EBS RAID configurations. However, in order to get persistent storage, one has to use network-attached EBS volumes, a sort of limitless in capacity but bound in I/O wonder of Amazon architecture. In order to use more disk space, Amazon provides ephemeral disks that one can format and mount anywhere on the file system. Up until very recently, root directories (’/’) at EC2 were limited to 10Gb, a limit defined by the maximum size of an Amazon Machine Image (AMI), essentially a template of an EC2 instance. Many customers, as well as services like Amazon Aurora, build highly durable and available systems on local instance storage.Amazon’s EC2 service is really neat, but its disk subsystem has some peculiarities that are not initially obvious. Still, there is a misconception that data on local instance store volumes (both the more "classic" HDD or SSD volumes that are virtualized by Xen, as well as the new generation of local NVMe storage) could vanish due to this vestigial term that lingers in the API. By 2010 we had transitioned to using "instance storage" in the documentation, which included a big note about how the data remains if an instance reboots for any reason (planned or unplanned). Data written to local storage is not transient, fleeting, or short lived. The "ephemeral" term confuses a lot of customers, and that's why we stopped using it. I don't know exactly when we stopped using "ephemeral" in our documentation, but I think it was with the introduction of EBS around 2008. Unfortunately it is part of the EC2 API for the block device mapping of the "classic" instance store interfaces on the Xen platform. ![]()
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