google-compute-engine - Google Compute Engine VM 磁盘非常慢

Question

我们刚刚切换到 Google Compute Engine，但在磁盘速度方面遇到了重大问题。它大约是 Linode 的 5% 或更糟。写入从未超过20M/s，读取从未超过10M/s。大多数情况下，写入速度为 15M/s，读取速度为 5M/s。

我们目前正在运行 n1-highmem-4 (4 个 vCPU，26 GB 内存)机器。 CPU和内存不是瓶颈。只需运行一个脚本，从 PostgreSQL 数据库读取行，处理它们，然后写回 PostgreSQL。批量更新数据库行只是一个常见的工作。尝试运行20个进程以利用多核，但总体进展仍然缓慢。

我们认为磁盘可能是瓶颈，因为流量异常低。

最后我们决定做基准测试。我们发现它不仅速度慢，而且似乎有一个可重现的主要错误:

创建并连接到实例

至少运行基准测试 3 次:

dd if=/dev/zero bs=1024 count=5000000 of=~/5Gb.file

我们发现它变得非常缓慢，根本无法完成基准测试。

Answer 1

Persistent Disk 的性能与磁盘本身的大小和它所连接的 VM 的大小成正比。磁盘(或VM)越大，性能就越高，因此本质上，您为磁盘或VM支付的价格不仅是磁盘/CPU/RAM，还有IOPS和吞吐量。

引用 Persistent Disk documentation :

Persistent disk performance depends on the size of the volume and the type of disk you select. Larger volumes can achieve higher I/O levels than smaller volumes. There are no separate I/O charges as the cost of the I/O capability is included in the price of the persistent disk.

Persistent disk performance can be described as follows:

• IOPS performance limits grow linearly with the size of the persistent disk volume.
• Throughput limits also grow linearly, up to the maximum bandwidth for the virtual machine that the persistent disk is attached to.
• Larger virtual machines have higher bandwidth limits than smaller virtual machines.

页面上还有一个更详细的定价图表，显示您购买的每 GB 空间所获得的 yield (以下数据是截至 2014 年 8 月的最新数据):

                                  Standard disks     SSD persistent disks

Price (USD/GB per month)                $0.04               $0.025
Maximum Sustained IOPS
  Read IOPS/GB                           0.3                  30
  Write IOPS/GB                          1.5                  30
Read IOPS/volume per VM                 3,000               10,000
Write IOPS/volume per VM               15,000               15,000
Maximum Sustained Throughput
  Read throughput/GB (MB/s)              0.12                 0.48
  Write throughput/GB (MB/s)             0.09                 0.48
Read throughput/volume per VM (MB/s)     180                  240
Write throughput/volume per VM (MB/s)    120                  240

以及页面上特定大小的磁盘将为您提供的具体示例:

As an example of how you can use the performance chart to determine the disk volume you want, consider that a 500GB standard persistent disk will give you:

• (0.3 × 500) = 150 small random reads
• (1.5 × 500) = 750 small random writes
• (0.12 × 500) = 60 MB/s of large sequential reads
• (0.09 × 500) = 45 MB/s of large sequential writes