EBS (Elastic Block Store) provides block level storage. That is, it offers storage volumes that can be attached as filesystems, like traditional network drives.
EBS volumes can only be attached to one EC2 instance at a time. In contrast, EFS can be shared but has a much higher price point (a comparison).
⏱One can provision IOPS (that is, pay for a specific level of I/O operations per second) to ensure a particular level of performance for a disk.
⏱A single gp2 EBS volume allows 16k IOPS max To get the maximum performance out of a gp2 EBS volume, it has to be of a maximum size and attached to an EBS-optimized EC2 instance.
💸Standard and gp2 EBS volumes improve IOPS with size. It may make sense for you to simply enlarge a volume instead of paying for better performance explicitly. This can in many cases reduce costs by 2/3.
A standard block size for an EBS volume is 16kb.
EBS Gotchas and Limitations
❗EBS durability is reasonably good for a regular hardware drive (annual failure rate of between 0.1% - 0.2%). On the other hand, that is very poor if you don’t have backups! By contrast, S3 durability is extremely high. If you care about your data, back it up to S3 with snapshots.
🔸EBS has an SLA with 99.99% uptime. See notes on high availability below.
❗EBS volumes have a volume type indicating the physical storage type. The types called “standard” (st1 or sc1) are actually old spinning-platter disks, which deliver only hundreds of IOPS — not what you want unless you’re really trying to cut costs. Modern SSD-based gp2 or io1 are typically the options you want.
❗When restoring a snapshot to create an EBS volume, blocks are lazily read from S3 the first time they're referenced. To avoid an initial period of high latency, you may wish to use dd or fio as per the official documentation.