Amazon EBS Volume Types
Amazon EBS provides the following volume types, which differ in performance characteristics and price, so that you can tailor your storage performance and cost to the needs of your applications. The volumes types fall into two categories:
-
SSD-backed volumes optimized for transactional workloads involving frequent read/write operations with small I/O size, where the dominant performance attribute is IOPS
-
HDD-backed volumes optimized for large streaming workloads where throughput (measured in MiB/s) is a better performance measure than IOPS
There are several factors that can affect the performance of EBS volumes, such as instance configuration, I/O characteristics, and workload demand. For more information about getting the most out of your EBS volumes, see Amazon EBS Volume Performance on Windows Instances.
For more information about pricing, see Amazon EBS Pricing.
Volume Characteristics
The following table describes the use cases and performance characteristics for each
volume type. The default volume type is General Purpose SSD (gp2).
| Solid-State Drives (SSD) | Hard Disk Drives (HDD) | |||
|---|---|---|---|---|
| Volume Type | General Purpose SSD (gp2)
|
Provisioned IOPS SSD (io1)
|
Throughput Optimized HDD (st1)
|
Cold HDD (sc1)
|
| Description | General purpose SSD volume that balances price and performance for a wide variety of workloads | Highest-performance SSD volume for mission-critical low-latency or high-throughput workloads | Low-cost HDD volume designed for frequently accessed, throughput-intensive workloads | Lowest cost HDD volume designed for less frequently accessed workloads |
| Use Cases |
|
|
|
|
| API Name | gp2 |
io1 |
st1 |
sc1 |
| Volume Size | 1 GiB - 16 TiB | 4 GiB - 16 TiB | 500 GiB - 16 TiB | 500 GiB - 16 TiB |
| Max IOPS per Volume | 16,000 (16 KiB I/O) * | 64,000 (16 KiB I/O) † | 500 (1 MiB I/O) | 250 (1 MiB I/O) |
| Max Throughput per Volume | 250 MiB/s * | 1,000 MiB/s † | 500 MiB/s | 250 MiB/s |
| Max IOPS per Instance †† | 80,000 | 80,000 | 80,000 | 80,000 |
| Max Throughput per Instance †† | 2,375 MB/s | 2,375 MB/s | 2,375 MB/s | 2,375 MB/s |
| Dominant Performance Attribute | IOPS | IOPS | MiB/s | MiB/s |
* The throughput limit is between 128 MiB/s and 250 MiB/s, depending
on the volume size. Volumes smaller than 170 GiB deliver a maximum throughput of 128
MiB/s. Volumes larger than 170 GiB but smaller than 334 GiB deliver a maximum
throughput of 250 MiB/s if burst credits are available. Volumes larger
than or equal to 334 GiB deliver 250 MiB/s regardless of burst credits.
Older gp2 volumes might not reach full performance unless you modify the
volume. For more information, see Amazon EBS Elastic Volumes.
† Maximum IOPS and throughput are guaranteed only on
Nitro-based Instances.
Other instances guarantee up to 32,000 IOPS and
500 MiB/s. Older io1 volumes might not reach
full performance unless you modify the volume. For more information, see Amazon EBS Elastic Volumes.
†† To achieve this throughput, you must have an instance that supports EBS optimization.
Previous Generation Volume Types
The following table describes previous-generation EBS volume types. If you need higher
performance or performance consistency than previous-generation volumes can provide,
we
recommend that you consider using General Purpose SSD (gp2) or other current volume types. For more
information, see Previous Generation
Volumes.
| Hard Disk Drives (HDD) | |
|---|---|
| Volume Type | Magnetic |
| Use Cases | Workloads where data is infrequently accessed |
| API Name | standard |
| Volume Size | 1 GiB-1 TiB |
| Max IOPS per Volume | 40–200 |
| Max Throughput per Volume | 40–90 MiB/s |
| Max IOPS per Instance | 80,000 |
| Max Throughput per Instance | 1,750 MiB/s |
| Dominant Performance Attribute | IOPS |
General Purpose SSD (gp2) Volumes
General Purpose SSD (gp2) volumes offer cost-effective storage that is ideal for a broad range of
workloads. These volumes deliver single-digit millisecond latencies and the ability
to burst
to 3,000 IOPS for extended periods of time. Between a minimum of 100 IOPS
(at 33.33 GiB and below) and a maximum of 16,000 IOPS (at 5,334 GiB and above),
baseline performance scales linearly at 3 IOPS per GiB of volume size. AWS
designs gp2 volumes to deliver 90% of the provisioned performance 99% of the time. A gp2
volume can range in size from 1 GiB to 16 TiB.
I/O Credits and Burst Performance
The performance of gp2 volumes is tied to volume size, which determines the baseline
performance level of the volume and how quickly it accumulates I/O credits; larger
volumes
have higher baseline performance levels and accumulate I/O credits faster. I/O credits
represent the available bandwidth that your gp2 volume can use to burst large amounts of
I/O when more than the baseline performance is needed. The more credits your volume
has
for I/O, the more time it can burst beyond its baseline performance level and the
better
it performs when more performance is needed. The following diagram shows the burst-bucket
behavior for gp2.
Each volume receives an initial I/O credit balance of 5.4 million I/O credits, which
is enough to sustain the maximum burst performance of 3,000 IOPS for 30 minutes. This
initial credit balance is designed to provide a fast initial boot cycle for boot volumes
and to provide a good bootstrapping experience for other applications. Volumes earn
I/O
credits at the baseline performance rate of 3 IOPS per GiB of volume
size. For example, a 100 GiB gp2 volume has a baseline performance of 300 IOPS.
When your volume requires more than the baseline performance I/O level, it draws on I/O credits in the credit balance to burst to the required performance level, up to a maximum of 3,000 IOPS. When your volume uses fewer I/O credits than it earns in a second, unused I/O credits are added to the I/O credit balance. The maximum I/O credit balance for a volume is equal to the initial credit balance (5.4 million I/O credits).
When the baseline performance of a volume is higher than maximum burst performance, I/O credits are never spent. If the volume is attached to a Nitro-based instance, the burst balance is not reported. For a non-Nitro-based instance, the reported burst balance is 100%.
The burst duration of a volume is dependent on the size of the volume, the burst IOPS required, and the credit balance when the burst begins. This is shown in the following equation:
(Credit balance) Burst duration = ------------------------------------ (Burst IOPS) - 3(Volume size in GiB)
The following table lists several volume sizes and the associated baseline performance of the volume (which is also the rate at which it accumulates I/O credits), the burst duration at the 3,000 IOPS maximum (when starting with a full credit balance), and the time in seconds that the volume would take to refill an empty credit balance.
|
Volume size (GiB) |
Baseline performance (IOPS) |
Burst duration when driving sustained 3,000 IOPS (second) |
Seconds to fill empty credit balance when driving no IO |
|---|---|---|---|
|
1 |
100 |
1802 |
54,000 |
|
100 |
300 |
2,000 |
18,000 |
|
250 |
750 |
2,400 | 7,200 |
|
334 (Min. size for max throughput) |
1002 |
2703 |
5389 |
|
500 |
1,500 |
3,600 |
3,600 |
|
750 |
2,250 |
7,200 |
2,400 |
|
1,000 |
3,000 |
N/A* |
N/A* |
|
5,334 (Min. size for max IOPS) |
16,000 |
N/A* |
N/A* |
|
16,384 (16 TiB, max volume size) |
16,000 |
N/A* |
N/A* |
* The baseline performance of the volume exceeds the maximum burst performance.
What happens if I empty my I/O credit balance?
If your gp2 volume uses all of its I/O credit balance, the maximum IOPS
performance of the volume remains at the baseline IOPS performance level (the rate
at
which your volume earns credits) and the volume's maximum throughput is reduced to
the
baseline IOPS multiplied by the maximum I/O size. Throughput can never exceed
250 MiB/s. When I/O demand drops below the baseline level and unused
credits are added to the I/O credit balance, the maximum IOPS performance of the volume
again exceeds the baseline. For example, a 100 GiB gp2 volume with an empty credit
balance has a baseline performance of 300 IOPS and a throughput limit of 75 MiB/s
(300
I/O operations per second * 256 KiB per I/O operation = 75 MiB/s). The larger a volume
is, the greater the baseline performance is and the faster it replenishes the credit
balance. For more information about how IOPS are measured, see I/O Characteristics and Monitoring.
If you notice that your volume performance is frequently limited to the baseline level
(due to an empty I/O credit balance), you should consider using a larger gp2 volume
(with a higher baseline performance level) or switching to an io1 volume for workloads
that require sustained IOPS performance greater than 16,000 IOPS.
For information about using CloudWatch metrics and alarms to monitor your burst bucket balance, see Monitoring the Burst Bucket Balance for gp2, st1, and sc1 Volumes.
Throughput Performance
Throughput for a gp2 volume can be calculated using the following formula, up to the
throughput limit of 250 MiB/s:
Throughput in MiB/s = ((Volume size in GiB) × (IOPS per GiB) × (I/O size in KiB))
Assuming V = volume size, I = I/O size, R = I/O rate, and T = throughput, this can be simplified to:
T = VIR
The smallest volume size that achieves the maximum throughput is given by:
T V = ----- I R 250 MiB/s = --------------------- (256 KiB)(3 IOPS/GiB) [(250)(2^20)(Bytes)]/s = ------------------------------------------ (256)(2^10)(Bytes)([3 IOP/s]/[(2^30)(Bytes)]) (250)(2^20)(2^30)(Bytes) = ------------------------ (256)(2^10)(3) = 357,913,941,333 Bytes = 333⅓ GiB (334 GiB in practice because volumes are provisioned in whole gibibytes)
Provisioned IOPS SSD (io1) Volumes
Provisioned IOPS SSD (io1) volumes are designed to meet the needs of I/O-intensive workloads,
particularly database workloads, that are sensitive to storage performance and consistency.
Unlike gp2, which uses a bucket and credit model to calculate performance, an io1 volume
allows you to specify a consistent IOPS rate when you create the volume, and Amazon
EBS delivers
the provisioned IOPS performance 99.9 percent of the time.
An io1 volume can range in size from 4 GiB to 16 TiB. You can provision from 100 IOPS
up to 64,000 IOPS per volume on Nitro-based Instances instances and up to 32,000 on other
instances. The maximum
ratio of provisioned IOPS to requested volume size (in GiB) is 50:1. For example,
a 100 GiB volume can be provisioned with up to 5,000 IOPS. On a supported instance
type, any
volume 1,280 GiB in size or greater allows provisioning up to the 64,000
IOPS maximum (50 × 1,280 GiB = 64,000).
An io1 volume provisioned with up to 32,000 IOPS supports a maximum I/O size of 256
KiB and yields as much as 500 MiB/s of throughput. With the I/O size at the maximum,
peak
throughput is reached at 2,000 IOPS. A volume provisioned with more than 32,000 IOPS
(up to
the cap of 64,000 IOPS) supports a maximum I/O size of 16 KiB and yields as much as
1,000
MiB/s of throughput. The following graph illustrates these performance
characteristics:
Your per-I/O latency experience depends on the IOPS provisioned and your workload pattern. For the best per-I/O latency experience, we recommend that you provision an IOPS-to-GiB ratio greater than 2:1. For example, a 2,000 IOPS volume should be smaller than 1,000 GiB.
Note
Some AWS accounts created before 2012 might have access to Availability Zones in
us-west-1 or ap-northeast-1 that do not support Provisioned IOPS SSD (io1) volumes. If
you are unable to create an io1 volume (or launch an instance with an io1
volume in its block device mapping) in one of these Regions, try a different Availability
Zone in the Region. You can verify that an Availability Zone supports io1 volumes
by creating a 4 GiB io1 volume in that zone.
Throughput Optimized HDD (st1) Volumes
Throughput Optimized HDD (st1) volumes provide low-cost magnetic storage that defines performance
in terms of throughput rather than IOPS. This volume type is a good fit for large,
sequential workloads such as Amazon EMR, ETL, data warehouses, and log processing.
Bootable st1
volumes are not supported.
Throughput Optimized HDD (st1) volumes, though similar to Cold HDD (sc1) volumes, are designed to
support frequently accessed data.
This volume type is optimized for workloads involving large, sequential I/O, and we
recommend that customers with workloads performing small, random I/O use gp2. For more
information, see Inefficiency of Small Read/Writes on
HDD.
Throughput Credits and Burst Performance
Like gp2, st1 uses a burst-bucket model for performance. Volume size determines
the baseline throughput of your volume, which is the rate at which the volume accumulates
throughput credits. Volume size also determines the burst throughput of your volume,
which
is the rate at which you can spend credits when they are available. Larger volumes
have
higher baseline and burst throughput. The more credits your volume has, the longer
it can
drive I/O at the burst level.
The following diagram shows the burst-bucket behavior for st1.
Subject to throughput and throughput-credit caps, the available throughput of an st1
volume is expressed by the following formula:
(Volume size) x (Credit accumulation rate per TiB) = Throughput
For a 1-TiB st1 volume, burst throughput is limited to 250 MiB/s, the bucket fills
with credits at 40 MiB/s, and it can hold up to 1 TiB-worth of credits.
Larger volumes scale these limits linearly, with throughput capped at a maximum of 500 MiB/s. After the bucket is depleted, throughput is limited to the baseline rate of 40 MiB/s per TiB.
On volume sizes ranging from 0.5 to 16 TiB, baseline throughput varies from 20 to a cap of 500 MiB/s, which is reached at 12.5 TiB as follows:
40 MiB/s 12.5 TiB x ---------- = 500 MiB/s 1 TiB
Burst throughput varies from 125 MiB/s to a cap of 500 MiB/s, which is reached at 2 TiB as follows:
250 MiB/s 2 TiB x ---------- = 500 MiB/s 1 TiB
The following table states the full range of base and burst throughput values for
st1:
| Volume Size (TiB) | ST1 Base Throughput (MiB/s) | ST1 Burst Throughput (MiB/s) |
|---|---|---|
| 0.5 | 20 | 125 |
| 1 | 40 | 250 |
| 2 | 80 | 500 |
| 3 | 120 | 500 |
| 4 | 160 | 500 |
| 5 | 200 | 500 |
| 6 | 240 | 500 |
| 7 | 280 | 500 |
| 8 | 320 | 500 |
| 9 | 360 | 500 |
| 10 | 400 | 500 |
| 11 | 440 | 500 |
| 12 | 480 | 500 |
| 12.5 | 500 | 500 |
| 13 | 500 | 500 |
| 14 | 500 | 500 |
| 15 | 500 | 500 |
| 16 | 500 | 500 |
The following diagram plots the table values:
Note
When you create a snapshot of a Throughput Optimized HDD (st1) volume, performance may drop as
far as the volume's baseline value while the snapshot is in progress.
For information about using CloudWatch metrics and alarms to monitor your burst bucket balance, see Monitoring the Burst Bucket Balance for gp2, st1, and sc1 Volumes.
Cold HDD (sc1) Volumes
Cold HDD (sc1) volumes provide low-cost magnetic storage that defines performance in
terms of throughput rather than IOPS. With a lower throughput limit than st1, sc1 is a
good fit for large, sequential cold-data workloads. If you require infrequent access
to your data and are looking to save costs, sc1 provides inexpensive block storage.
Bootable sc1 volumes are not supported.
Cold HDD (sc1) volumes, though similar to Throughput Optimized HDD (st1) volumes, are designed to
support infrequently accessed data.
Note
This volume type is optimized for workloads involving large, sequential I/O, and we
recommend that customers with workloads performing small, random I/O use gp2. For more
information, see Inefficiency of Small Read/Writes on
HDD.
Throughput Credits and Burst Performance
Like gp2, sc1 uses a burst-bucket model for performance. Volume size determines
the baseline throughput of your volume, which is the rate at which the volume accumulates
throughput credits. Volume size also determines the burst throughput of your volume,
which
is the rate at which you can spend credits when they are available. Larger volumes
have
higher baseline and burst throughput. The more credits your volume has, the longer
it can
drive I/O at the burst level.
Subject to throughput and throughput-credit caps, the available throughput of an sc1
volume is expressed by the following formula:
(Volume size) x (Credit accumulation rate per TiB) = Throughput
For a 1-TiB sc1 volume, burst throughput is limited to 80 MiB/s, the bucket fills
with credits at 12 MiB/s, and it can hold up to 1 TiB-worth of credits.
Larger volumes scale these limits linearly, with throughput capped at a maximum of 250 MiB/s. After the bucket is depleted, throughput is limited to the baseline rate of 12 MiB/s per TiB.
On volume sizes ranging from 0.5 to 16 TiB, baseline throughput varies from 6 MiB/s to a maximum of 192 MiB/s, which is reached at 16 TiB as follows:
12 MiB/s 16 TiB x ---------- = 192 MiB/s 1 TiB
Burst throughput varies from 40 MiB/s to a cap of 250 MiB/s, which is reached at 3.125 TiB as follows:
80 MiB/s 3.125 TiB x ----------- = 250 MiB/s 1 TiB
The following table states the full range of base and burst throughput values for
sc1:
| Volume Size (TiB) | SC1 Base Throughput (MiB/s) | SC1 Burst Throughput (MiB/s) |
|---|---|---|
| 0.5 | 6 | 40 |
| 1 | 12 | 80 |
| 2 | 24 | 160 |
| 3 | 36 | 240 |
| 3.125 | 37.5 | 250 |
| 4 | 48 | 250 |
| 5 | 60 | 250 |
| 6 | 72 | 250 |
| 7 | 84 | 250 |
| 8 | 96 | 250 |
| 9 | 108 | 250 |
| 10 | 120 | 250 |
| 11 | 132 | 250 |
| 12 | 144 | 250 |
| 13 | 156 | 250 |
| 14 | 168 | 250 |
| 15 | 180 | 250 |
| 16 | 192 | 250 |
The following diagram plots the table values:
Note
When you create a snapshot of a Cold HDD (sc1) volume, performance may drop as far
as the volume's baseline value while the snapshot is in progress.
For information about using CloudWatch metrics and alarms to monitor your burst bucket balance, see Monitoring the Burst Bucket Balance for gp2, st1, and sc1 Volumes.
Magnetic (standard)
Magnetic volumes are backed by magnetic drives and are suited for workloads where data is accessed infrequently, and scenarios where low-cost storage for small volume sizes is important. These volumes deliver approximately 100 IOPS on average, with burst capability of up to hundreds of IOPS, and they can range in size from 1 GiB to 1 TiB.
Note
Magnetic is a Previous Generation Volume. For new applications, we recommend using one of the newer volume types. For more information, see Previous Generation Volumes.
For information about using CloudWatch metrics and alarms to monitor your burst bucket balance, see Monitoring the Burst Bucket Balance for gp2, st1, and sc1 Volumes.
Performance Considerations When Using HDD Volumes
For optimal throughput results using HDD volumes, plan your workloads with the following considerations in mind.
Throughput Optimized HDD vs. Cold HDD
The st1 and sc1 bucket sizes vary according to volume size, and a full bucket
contains enough tokens for a full volume scan. However, larger st1 and sc1 volumes
take longer for the volume scan to complete due to per-instance and per-volume throughput
limits. Volumes attached to smaller instances are limited to the per-instance throughput
rather than the st1 or sc1 throughput limits.
Both st1 and sc1 are designed for performance consistency of 90% of burst
throughput 99% of the time. Non-compliant periods are approximately uniformly distributed,
targeting 99% of expected total throughput each hour.
The following table shows ideal scan times for volumes of various size, assuming full buckets and sufficient instance throughput.
In general, scan times are expressed by this formula:
Volume size ------------- = Scan time Throughput
For example, taking the performance consistency guarantees and other optimizations
into account, an st1 customer with a 5-TiB volume can expect to complete a full volume
scan in 2.91 to 3.27 hours.
5 TiB 5 TiB ----------- = ------------------- = 10,486 s = 2.91 hours (optimal) 500 MiB/s 0.00047684 TiB/s 2.91 hours 2.91 hours + -------------- = 3.27 hours (minimum expected) (0.90)(0.99) <-- From expected performance of 90% of burst 99% of the time
Similarly, an sc1 customer with a 5-TiB volume can expect to complete a full volume
scan in 5.83 to 6.54 hours.
5 TiB ------------------- = 20972 s = 5.83 hours (optimal) 0.000238418 TiB/s 5.83 hours -------------- = 6.54 hours (minimum expected) (0.90)(0.99)
| Volume Size (TiB) | ST1 Scan Time with Burst (Hours)* | SC1 Scan Time with Burst (Hours)* |
|---|---|---|
| 1 | 1.17 | 3.64 |
| 2 | 1.17 | 3.64 |
| 3 | 1.75 | 3.64 |
| 4 | 2.33 | 4.66 |
| 5 | 2.91 | 5.83 |
| 6 | 3.50 | 6.99 |
| 7 | 4.08 | 8.16 |
| 8 | 4.66 | 9.32 |
| 9 | 5.24 | 10.49 |
| 10 | 5.83 | 11.65 |
| 11 | 6.41 | 12.82 |
| 12 | 6.99 | 13.98 |
| 13 | 7.57 | 15.15 |
| 14 | 8.16 | 16.31 |
| 15 | 8.74 | 17.48 |
| 16 | 9.32 | 18.64 |
* These scan times assume an average queue depth (rounded to the nearest whole number) of four or more when performing 1 MiB of sequential I/O.
Therefore if you have a throughput-oriented workload that needs to complete scans
quickly (up to 500 MiB/s), or requires several full volume scans a day, use st1. If you
are optimizing for cost, your data is relatively infrequently accessed, and you don’t
need
more than 250 MiB/s of scanning performance, then use sc1.
Inefficiency of Small Read/Writes on HDD
The performance model for st1 and sc1 volumes is optimized for sequential I/Os,
favoring high-throughput workloads, offering acceptable performance on workloads with
mixed IOPS and throughput, and discouraging workloads with small, random I/O.
For example, an I/O request of 1 MiB or less counts as a 1 MiB I/O credit. However, if the I/Os are sequential, they are merged into 1 MiB I/O blocks and count only as a 1 MiB I/O credit.
Limitations on per-Instance Throughput
Throughput for st1 and sc1 volumes is always determined by the smaller of the
following:
-
Throughput limits of the volume
-
Throughput limits of the instance
As for all Amazon EBS volumes, we recommend that you select an appropriate EBS-optimized EC2 instance in order to avoid network bottlenecks. For more information, see Amazon EBS–Optimized Instances.
Monitoring the Burst Bucket Balance for gp2,
st1, and sc1 Volumes
You can monitor the burst-bucket level for gp2, st1, and sc1 volumes using the EBS
BurstBalance metric available in Amazon CloudWatch. This metric shows the percentage
of I/O credits (for gp2) or throughput credits (for st1 and sc1) remaining in the
burst bucket. For more information about the BurstBalance metric and other
metrics related to I/O, see I/O Characteristics and Monitoring.
CloudWatch also allows you to set an alarm that notifies
you when the BurstBalance value falls to a certain level. For more information,
see Creating Amazon CloudWatch
Alarms.
