How do I troubleshoot iSCSI storage performance issues?
How do I troubleshoot iSCSI storage performance issues?
Symptoms
When you encounter an issue with iSCSI storage performance, we encourage you to perform basic troubleshooting with the instructions in this article. There are several possible issues you may encounter:
- Low throughput
- High latency
- Other storage, system, or network issues
Resolution
To troubleshoot a low throughput:
If you think the throughput is lower than expected when checking Windows File Explorer, we suggest that you try different benchmarking tools and refer to the information below.
Understanding your benchmark index:
The performance tests of Synology NAS products are conducted using IOMeter as the benchmarking tool and SSDs as the storage media, and multiple workers and threads are running to maximize the throughput of the iSCSI storage. If you use Windows File Explorer to copy a file from one location to another, the speed displayed at the Windows UI may not reflect the actual capability of the iSCSI storage.
To troubleshoot a high latency:
If your applications (virtual machines or application servers) experience a high latency (larger than 30 ms in general), follow the steps below to identify the root cause:
- Go to DSM > Resource Monitor > Performance > iSCSI (For DSM 7.0, the tab is renamed as LUN).
- Click Choose Charts.
- Check Disk Latency and Network Latency, and click OK.
- You will then discover what contributes to the iSCSI storage latency. Usually it is the disk.
- If the disk latency is too high, please go through Checklist 1 to check the storage status.
- If the network latency is too high, please go through Checklist 2 to check the iSCSI network environment.
To troubleshoot issues with the storage, system, or network:
Go through the following checklists to identify possible root causes of compromised performance.
Checklist 1: Storage and system
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Item
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What to do
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Why
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|---|---|---|
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RAID/volume health
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Instead doing any rebuilding, repairing, or expanding in Storage Manager, check if the status of each of the following items is normal and in good health:
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HDD/SSD health
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Check if the HDDs or SSDs are healthy at Storage Manager > HDD/SDD.
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Defective drives might hinder the full utilization of the storage system.
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System status
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Examine the CPU and disk utilization in Resource Monitor, or disable all the services except for the ones that you would like to run at Control Panel > Info Center > Service.
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To make sure no resource-intensive processes are running on your Synology NAS.
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Checklist 2: Storage and network
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Item
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What to do
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Why
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|---|---|---|
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Multipath I/O settings
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Make sure MPIO is set up properly on your hosts. Refer to the following tutorials:
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It is recommended that you configure MPIO instead of network bonding (or Link Aggregation) to maximize the throughput for all hosts. Also, the stability and performance of MPIO configuration have been thoroughly verified before product and software update releases.
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iSCSI network
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Make sure the iSCSI network is isolated and is a dedicated VLAN. Isolate iSCSI traffic from other traffics, such as file transfer or virtual machines.
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Mixing the iSCSI traffic with other network traffics is not recommended because it will complicate the troubleshooting process with additional unknown factors.
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iSCSI HBA
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If you are using a hardware iSCSI initiator, try software iSCSI initiators and compare the performances.
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Our iSCSI storage service is verified with the following iSCSI initiators:
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