Configure disks to meet performance requirements

Overview

This page discusses the many factors that determine the performance of the block storage volumes that you attach to your virtual machine (VM) instances. Before you begin, consider the following:

• Persistent disks are networked storage and generally have higher latency compared to physical disks or local SSDs. To reach the maximum performance limits of your persistent disks, you must issue enough I/O requests in parallel. To check if you're using a high enough queue depth to reach your required performance levels, see I/O queue depth.

• Make sure that your application is issuing enough I/Os to saturate your disk.

• For workloads that primarily involve small (from 4 KB to 16 KB) random I/Os, the limiting performance factor is random input/output operations per second (IOPS).

• For workloads that primarily involve sequential or large (256 KB to 1 MB) random I/Os, the limiting performance factor is throughput.

Choose a storage option

To choose a block storage option that is appropriate for your workload, consider factors such as machine type support, disk size, and performance limits.

Disk types

You can provide several different types of block storage for your instances to use. When you configure a zonal or regional persistent disk, you can select one of the following disk types. If you create a disk in the Google Cloud console, the default disk type is pd-balanced. If you create a disk using the gcloud CLI or the Compute Engine API, the default disk type is pd-standard.

• Standard persistent disks (pd-standard) are suited for large data processing workloads that primarily use sequential I/Os.
• Balanced persistent disks (pd-balanced) are an alternative to SSD persistent disks that balance performance and cost. With the same maximum IOPS as SSD persistent disks and lower IOPS per GB, a balanced persistent disk offers performance levels suitable for most general-purpose applications at a price point between that of standard and SSD persistent disks.
• SSD persistent disks (pd-ssd) are suited for enterprise applications and high-performance database needs that require lower latency and more IOPS than standard persistent disks provide. SSD persistent disks are designed for single-digit millisecond latencies; the observed latency is app specific.
• Extreme persistent disks (pd-extreme) offer consistently high performance for both random access workloads and bulk throughput. They are designed for high-end database workloads, such as Oracle or SAP HANA. Unlike other disk types, you can provision your desired IOPS. For more information, see Extreme persistent disks.

Performance limits

The following table shows performance limits for persistent disks. For information about local SSD performance limits, see Local SSD performance.

Zonal persistent disks

The following table shows maximum sustained IOPS for zonal persistent disks:

	Zonal standard PD	Zonal balanced PD	Zonal SSD PD	Zonal extreme PD	Zonal SSD PD multi-writer mode
Read IOPS per GB	0.75	6	30	–	30
Write IOPS per GB	1.5	6	30	–	30
Read IOPS per instance	7,500^*	80,000^*	100,000^*	120,000^*	100,000^*
Write IOPS per instance	15,000^*	80,000^*	100,000^*	120,000^*	100,000^*

The following table shows maximum sustained throughput for zonal persistent disks:

	Zonal standard PD	Zonal balanced PD	Zonal SSD PD	Zonal extreme PD	Zonal SSD PD multi-writer mode
Throughput per GB (MB/s)	0.12	0.28	0.48	–	0.48
Read throughput per instance (MB/s)	1,200^*	1,200^*	1,200^*	2,200^**	1,200^**
Write throughput per instance (MB/s)	400^**	1,200^*	1,200^*	2,200^**	1,200^**

^* Persistent disk IOPS and throughput performance depends on disk size, instance vCPU count, and I/O block size, among other factors.

Regional persistent disks

The following table shows maximum sustained IOPS for regional persistent disks:

	Regional standard PD	Regional balanced PD	Regional SSD PD
Read IOPS per GB	0.75	6	30
Write IOPS per GB	1.5	6	30
Read IOPS per instance	7,500^*	60,000^*	60,000^*
Write IOPS per instance	15,000^*	30,000^*	30,000^*

The following table shows maximum sustained throughput for regional persistent disks:

	Regional standard PD	Regional balanced PD	Regional SSD PD
Throughput per GB (MB/s)	0.12	0.28	0.48
Read throughput per instance	1,200^*	1,200^*	1,200^*
Write throughput per instance	200^**	600^*	600^*

^* Persistent disk IOPS and throughput performance depends on disk size, instance vCPU count, and I/O block size, among other factors.

Attaching a disk to multiple virtual machine instances in read-only mode mode or in multi-writer mode does not affect aggregate performance or cost. Each machine gets a share of the per-disk performance limit. Persistent disks created in multi-writer mode have specific IOPS and throughput limits. To learn how to share persistent disks between multiple VMs, see Sharing persistent disks between VMs.

Persistent disk I/O operations share a common path with vNIC network traffic within your VM's hypervisor. Therefore, if your VM has significant network traffic, the actual read bandwidth and IOPS consistency might be less than the listed maximum limits. Some variability in the performance limits is to be expected, especially when operating near the maximum IOPS limits with an I/O size of 16 KB. For a summary of bandwidth expectations, see Bandwidth summary table.

Configure your persistent disks and instances

Persistent disk performance scales with the size of the disk and with the number of vCPUs on your VM instance.

Performance scales until it reaches either the limits of the disk or the limits of the VM instance to which the disk is attached. The machine type and the number of vCPUs on the instance determine the VM instance limits.

The following tables show performance limits for zonal persistent disks. For performance limits for regional persistent disks, see Regional persistent disk performance.

Performance by machine type and vCPU count

The following tables show how zonal persistent disk performance varies according to the machine type and number of vCPUs on the VM to which the disk is attached.

A2 VMs

pd-standard

Machine type	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
a2-highgpu-1g	15,000	5,000	400	800
a2-highgpu-2g	15,000	7,500	400	1,200
a2-highgpu-4g	15,000	7,500	400	1,200
a2-highgpu-8g	15,000	7,500	400	1,200
a2-megagpu-16g	15,000	7,500	400	1,200

pd-balanced

Machine type	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
a2-highgpu-1g	15,000	15,000	800	800
a2-highgpu-2g	20,000	20,000	1,200	1,200
a2-highgpu-4g	50,000	50,000	1,200	1,200
a2-highgpu-8g	80,000	80,000	1,200	1,200
a2-megagpu-16g	80,000	80,000	1,200	1,200

pd-performance

Machine type	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
a2-highgpu-1g	15,000	15,000	800	800
a2-highgpu-2g	25,000	25,000	1,200	1,200
a2-highgpu-4g	60,000	60,000	1,200	1,200
a2-highgpu-8g	100,000	100,000	1,200	1,200
a2-megagpu-16g	100,000	100,000	1,200	1,200

C2 VMs

pd-standard

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
4	4,000	3,000	240	240
8	4,000	3,000	240	240
16	4,000	3,000	240	240
30	8,000	3,000	240	240
60	15,000	3,000	240	240

pd-balanced

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
4	4,000	4,000	240	240
8	4,000	4,000	240	240
16	4,000	8,000	480	600
30	8,000	15,000	480	600
60	15,000	15,000	800	1,200

pd-performance

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
4	4,000	4,000	240	240
8	4,000	4,000	240	240
16	4,000	8,000	480	600
30	8,000	15,000	480	600
60	15,000	30,000	800	1,200

C2D VMs

pd-standard

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
2	4,590	3,060	245	245
4	4,590	3,060	245	245
8	4,590	3,060	245	245
16	4,590	3,060	245	245
32	8,160	3,060	245	245
56	8,160	3,060	245	245
112	15,300	3,060	245	245

pd-balanced

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
2	4,590	4,080	245	245
4	4,590	4,080	245	245
8	4,590	4,080	245	245
16	4,590	8,160	245	326
32	8,160	15,300	245	612
56	8,160	15,300	245	612
112	15,300	30,600	408	1,224

pd-performance

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
2	4,590	4,080	245	245
4	4,590	4,080	245	245
8	4,590	4,080	245	245
16	4,590	8,160	245	326
32	8,160	15,300	245	612
56	8,160	15,300	245	612
112	15,300	30,600	408	1,224

E2 VMs

pd-standard

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
e2-medium^*	10,000	1,000	200	200
2-7	15,000	3,000	240	240
8-15	15,000	5,000	400	800
16 or more	15,000	7,500	400	1,200

^*E2 shared-core machine types run two vCPUs simultaneously shared on one physical core for a specific fraction of time.

pd-balanced

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
e2-medium^*	10,000	12,000	200	200
2-7	15,000	15,000	240	240
8-15	15,000	15,000	800	800
16-31	20,000	20,000	1,000	1,200
32 or more	50,000	50,000	1,000	1,200

^*E2 shared-core machine types run two vCPUs simultaneously shared on one physical core for a specific fraction of time.

pd-performance

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
e2-medium^*	10,000	12,000	200	200
2-7	15,000	15,000	240	240
8-15	15,000	15,000	800	800
16-31	25,000	25,000	1,000	1,200
32 or more	60,000	60,000	1,000	1,200

^*E2 shared-core machine types run two vCPUs simultaneously shared on one physical core for a specific fraction of time.

N1 VMs

pd-standard

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
1	15,000	Up to 3,000	204	240
2-7	15,000	3,000	240	240
8-15	15,000	5,000	400	800
16 or more	15,000	7,500	400	1,200

pd-balanced

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
1	15,000	15,000	204	240
2-7	15,000	15,000	240	240
8-15	15,000	15,000	800	800
16-31	20,000	20,000	1,200	1,200
32-63	50,000	50,000	1,200	1,200
64 or more	80,000	80,000	1,200	1,200

pd-performance

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
1	15,000	15,000	204	240
2-7	15,000	15,000	240	240
8-15	15,000	15,000	800	800
16-31	25,000	25,000	1,200	1,200
32-63	60,000	60,000	1,200	1,200
64 or more	100,000	100,000	1,200	1,200

N2 VMs

pd-standard

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
2-7	15,000	3,000	240	240
8-15	15,000	5,000	400	800
16 or more	15,000	7,500	400	1,200

pd-balanced

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
2-7	15,000	15,000	240	240
8-15	15,000	15,000	800	800
16-31	20,000	20,000	1,200	1,200
32-63	50,000	50,000	1,200	1,200
64 or more	80,000	80,000	1,200	1,200

pd-performance

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
2-7	15,000	15,000	240	240
8-15	15,000	15,000	800	800
16-31	25,000	25,000	1,200	1,200
32-63	60,000	60,000	1,200	1,200
64 or more	100,000	100,000	1,200	1,200

pd-extreme

Machine type	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
n2-standard-64	120,000	120,000	2,200	2,200
n2-highmem-64	120,000	120,000	2,200	2,200
n2-highmem-80	120,000	120,000	2,200	2,200

N2D VMs

pd-standard

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
2-7	15,000	3,000	240	240
8-15	15,000	5,000	400	800
16 or more	15,000	7,500	400	1,200

pd-balanced

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
2-7	15,000	15,000	240	240
8-15	15,000	15,000	800	800
16-31	20,000	20,000	1,200	1,200
32-63	50,000	50,000	1,200	1,200
64 or more	Up to 80,000	Up to 80,000	1,200	1,200

pd-performance

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
2-7	15,000	15,000	240	240
8-15	15,000	15,000	800	800
16-31	25,000	25,000	1,200	1,200
32-63	60,000	60,000	1,200	1,200
64 or more	Up to 100,000	Up to 100,000	1,200	1,200

M1 VMs

pd-standard

Machine type	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
m1-megamem-96	15,000	7,500	400	1,200
m1-ultramem-40	15,000	7,500	400	1,200
m1-ultramem-80	15,000	7,500	400	1,200
m1-ultramem-160	15,000	7,500	400	1,200

pd-balanced

Machine type	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
m1-megamem-96	80,000	80,000	1,200	1,200
m1-ultramem-40	60,000	60,000	1,200	1,200
m1-ultramem-80	70,000	70,000	1,200	1,200
m1-ultramem-160	70,000	70,000	1,200	1,200

pd-performance

Machine type	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
m1-megamem-96	90,000	90,000	1,200	1,200
m1-ultramem-40	60,000	60,000	1,200	1,200
m1-ultramem-80	70,000	70,000	1,200	1,200
m1-ultramem-160	70,000	70,000	1,200	1,200

pd-extreme

Machine type	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
m1-megamem-96	90,000	90,000	2,200	2,200

M2 VMs

pd-standard

Machine type	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
m2-megamem-416	15,000	7,500	400	1,200
m2-ultramem-208	15,000	7,500	400	1,200
m2-ultramem-416	15,000	7,500	400	1,200

pd-balanced

Machine type	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
m2-megamem-416	40,000	40,000	1,200	1,200
m2-ultramem-208	60,000	60,000	1,200	1,200
m2-ultramem-416	40,000	40,000	1,200	1,200

pd-performance

Machine type	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
m2-megamem-416	40,000	40,000	1,200	1,200
m2-ultramem-208	60,000	60,000	1,200	1,200
m2-ultramem-416	40,000	40,000	1,200	1,200

pd-extreme

Machine type	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
m2-ultramem-208	60,000	60,000	2,200	2,200
m2-ultramem-416	40,000	40,000	1,200	2,200

T2D VMs

pd-standard

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
1	15,000	3,000	204	240
2-7	15,000	3,000	240	240
8-15	15,000	5,000	400	800
16 or more	15,000	7,500	400	1,200

pd-balanced

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
1	15,000	15,000	204	240
2-7	15,000	15,000	240	240
8-15	15,000	15,000	800	800
16-31	20,000	20,000	1,200	1,200
32-63	50,000	50,000	1,200	1,200
64 or more	Up to 80,000	Up to 80,000	1,200	1,200

pd-performance

VM vCPU count	Maximum write IOPS	Maximum read IOPS	Maximum write throughput (MB/s)	Maximum read throughput (MB/s)
1	15,000	15,000	204	240
2-7	15,000	15,000	240	240
8-15	15,000	15,000	800	800
16-31	25,000	25,000	1,200	1,200
32-63	60,000	60,000	1,200	1,200
64 or more	Up to 100,000	Up to 100,000	1,200	1,200

Example

Consider a 1,000 GB zonal SSD persistent disk attached to a VM with an N2 machine type and 4 vCPUs. The read limit based solely on the size of the disk is 30,000 IOPS, because SSD persistent disks can reach up to 30 IOPS per GB of disk space. However, the VM has 4 vCPUs so the read limit is restricted to 15,000 IOPS.

Review performance and throttling metrics

You can review persistent disk performance metrics in Cloud Monitoring, Google Cloud's integrated monitoring solution.

If and when your disks are being throttled, several of these metrics are useful to understand. Throttling is intended to smooth out bursty I/Os. With throttling, bursty I/Os can be spread out over a period, so that the performance limits of your disk can be met but not exceeded at any given instant.

If your workload has a bursty I/O usage pattern, expect to see bursts in throttled bytes corresponding to bursts in read or written bytes. Similarly, expect to see bursts in throttled operations corresponding to bursts in read/write operations.

If your disk limit is 1,000 write IOPS, the disk accepts a write request every 1 millisecond. If you issue faster write requests, then a small delay is introduced to spread the requests 1 millisecond apart. The IOPS and throughput limits discussed in this document are enforced all the time, not on a per-minute or per-second basis.

Databases are a common example of bursty workloads. Databases tend to have short microbursts of I/O operations, which lead to temporary increases in queue depth. Higher queue depth can result in higher latency because more outstanding I/O operation requests are waiting in queue.

If your workload has a uniform I/O usage pattern and you are continuously reaching the performance limits of your disk, you can expect to see uniform levels of throttled bytes and operations.

To learn more, see Reviewing persistent disk performance metrics.

Optimize disk performance

To increase disk performance, start with the following steps:

• Resize your persistent disks to increase the per-disk IOPS and throughput limits. Persistent disks do not have any reserved, unusable capacity, so you can use the full disk without performance degradation. However, certain file system and applications might perform worse as the disk becomes full, so you might need to consider increasing the size of your disk to avoid such situations.

• Change the machine type and number of vCPUs on the instance to increase the per-instance IOPS and throughput limits.

After you ensure that any bottlenecks are not due to the disk size or machine type of the VM, your app and operating system might still need some tuning. See Optimizing persistent disk performance and Optimizing local SSD performance.

Other factors that affect performance

Network egress caps on write throughput

Your virtual machine (VM) instance has a network egress cap that depends on the machine type of the VM.

Compute Engine stores data on persistent disks with multiple parallel writes to ensure built-in redundancy. Also, each write request has some overhead that uses additional write bandwidth.

The maximum write traffic that a VM instance can issue is the network egress cap divided by a bandwidth multiplier that accounts for the write bandwidth used by this redundancy and overhead. The network egress cap depends on the machine type of the VM instance. The network egress caps for each machine type are listed in the Machine type tables in the Network egress bandwidth (Gbps) column.

In a situation where persistent disks compete with network egress bandwidth, 60% of the maximum network egress bandwidth, defined by the machine type, is allocated to persistent disk writes. The remaining 40% is available for all other network egress traffic. The following example shows how to calculate the maximum persistent disk write traffic that a VM instance can issue. Refer to egress bandwidth for details about other network egress traffic.

	Standard persistent disk			SSD persistent disk			Balanced persistent disk
Number of vCPUs	Write limit (MBps)	Write allocation (MBps)	Disk size needed to reach limit (GB)	Write limit (MBps)	Write allocation (MBps)	Disk size needed to reach limit (GB)	Write limit (MBps)	Write allocation (MBps)	Disk size needed to reach limit (GB)
1	72	43	600	204	122	425	204	122	729
2	240	227	2,000	240	227	500	240	227	858
4	240	227	2,000	240	227	500	240	227	858
6+	400	346	3,334	800	480	1667	800	480	2,858
16+	400	346	3,334	1,200	720	2,500	1,200	720	4,285

The bandwidth multiplier for standard persistent disks is 3.3x, which means the data is written out three times with a total overhead of 10%. The bandwidth multiplier for SSD persistent disks is 1.16 because the data is written out once with a total overhead of 16%. If you attach a disk to an N1 VM instance with 1 vCPU, the network egress cap is 2 gigabits per second (Gbps). You can calculate the ultimate bandwidth limit using the following formulas:

Standard persistent disk maximum write bandwidth for 1 vCPU
= 2 Gbps / 8 bits
= 0.25 GB per second = 250 MB per second => 250 MB per second / 3.35
~= 72 MB per second
SSD and balanced persistent disk maximum write bandwidth for 1 vCPU
= 2 Gbps / 8 bits
= 0.25 GB per second = 250 MB per second => 250 MB per second / 1.16
~= 204 MB per second

Using the write throughput per GB figures provided in the performance chart, you can also derive the required disk capacity to achieve this performance:

Required standard persistent disk size for maximum 1 vCPU write bandwidth
= 72 MB per second / 0.12 MB per second per GB
~= 600 GB
Required SSD persistent disk size for maximum 1 vCPU write bandwidth
= 204 MB per second / 0.48 MB per second per GB
~= 425 GB
Required balanced persistent disk size for maximum 1 vCPU write bandwidth
= 204 MB per second / 0.28 MB per second per GB
~= 729 GB

Similar to zonal persistent disks, write traffic from regional persistent disks contributes to the cumulative network egress cap of the instance. To calculate the available network egress for regional persistent disks, use a bandwidth multiplier of 6.6 for standard persistent disks and 2.32 for SSD and balanced persistent disks.

For 16+ core VMs, the maximum network egress bandwidth consumed by standard persistent disks is 1,320 MB per second (400 MBps * 3.3). For SSD persistent disks, the maximum network egress bandwidth consumed is 1,392 MB per second (1200 MBps * 1.16).

Simultaneous reads and writes

For standard persistent disks, simultaneous reads and writes share the same resources. While your instance is using more read throughput or IOPS, it is able to perform fewer writes. Conversely, instances that use more write throughput or IOPS are able to perform fewer reads.

Persistent disks cannot simultaneously reach their maximum throughput and IOPS limits for both reads and writes.

Note that throughput = IOPS * I/O size. To take advantage of maximum throughput limits for simultaneous reads and writes on SSD persistent disks, use an I/O size such that read and write IOPS combined don't exceed the IOPS limit.

Instance IOPS limits for simultaneous reads and writes

Standard persistent disk		SSD persistent disk (8 vCPUs)		SSD persistent disk (32+ vCPUs)		SSD persistent disk (64+ vCPUs)
Read	Write	Read	Write	Read	Write	Read	Write
7,500	0	15,000	0	60,000	0	100,000	0
5,625	3,750	11,250	3,750	45,000	15,000	75,000	25,000
3,750	7,500	7,500	7,500	30,000	30,000	50,000	50,000
1875	11,250	3,750	11,250	15,000	45,000	25,000	75,000
0	15,000	0	15,000	0	60,000	0	100,000

Instance throughput limits (MB per second) for simultaneous reads and writes

Standard persistent disk		SSD persistent disk (6-14 vCPUs)		SSD persistent disk (16+ vCPUs)
Read	Write	Read	Write	Read	Write
1200	0	800^*	800^*	1,200^*	1,200^*
900	100
600	200
300	300
0	400

^* For SSD persistent disks, the max read throughput and max write throughput are independent of each other, so these limits are constant.

The IOPS numbers in this table are based on an 8 KB I/O size. Other I/O sizes, such as 16 KB, might have different IOPS numbers but maintain the same read/write distribution.

Logical volume size

Persistent disks can be up to 64 TB in size, and you can create single logical volumes of up to 257 TB using logical volume management inside your VM. A larger volume size impacts performance in the following ways:

• Not all local file systems work well at this scale. Common operations, such as mounting and file system checking might take longer than expected.
• Maximum persistent disk performance is achieved at smaller sizes. Disks take longer to fully read or write with this much storage on one VM. If your application supports it, consider using multiple VMs for greater total-system throughput.
• Snapshotting large amounts of persistent disk might take longer than expected to complete and might provide an inconsistent view of your logical volume without careful coordination with your application.

Multiple disks attached to a single VM instance

Multiple disks of the same type

If you have multiple disks of the same type attached to a VM instance in the same mode (for example, read/write), the performance limits are the same as the limits of a single disk that has the combined size of those disks. If you use all the disks at 100%, the aggregate performance limit is split evenly among the disks regardless of relative disk size.

For example, suppose you have a 200 GB standard disk and a 1,000 GB standard disk. If you do not use the 1,000 GB disk, then the 200 GB disk can reach the performance limit of a 1,200 GB standard disk. If you use both disks at 100%, then each has the performance limit of a 600 GB standard persistent disk (1,200 GB / 2 disks = 600 GB disk).

Multiple disks of different types

If you have multiple disks of different types attached to a single VM, then the SSD per-VM limit determines the total performance limit for the VM. This total performance limit is shared between all disks attached to the VM.

For example, suppose you have one 5,000 GB standard disk and one 1,000 GB SSD disk attached to an N2 VM with one vCPU. The read IOPS limit for the standard disk is 3,000 and the read IOPS limit for the SSD disk is 15,000. Because the limit of the SSD disk determines the overall limit, the total read IOPS limit for your VM is 15,000. This limit is shared between all attached disks.

What's next

• Benchmark your persistent disks and local SSDs.
• Optimize your persistent disk and local SSD performance.
• Learn about persistent disk and local SSD pricing.
• Learn how to review your project log entries using the Logs Explorer.