ZFS7120 FC i/o problem with external disk shelf (pool-1)

Hi, All

Our Cu has ZFS7120.

1. 2TB*12 disks (on chassis-000)
2. 600GB*24 disks (on chassis-001 / DS2 with extension)
3. 96GB Logzila PCIe.
4. 7120 was used for SAN. FC HBAs on chassis-000.

There are two pools.

pool-0 is configured with 2TB*12ea. 48GB SSD with mirror. pool-0 was RAIDZ2.
pool-1 is oonfigured with 600GB*24ea. 48GB SSD with mirror. pool-1 was RAIDZ2.
Host Server is Windows2008 R2. (mpio setting).
Two pools has each LUN for SAN.

Two LUNs have 64KB recordsize. (same condition).

Symptom.
The I/O was normal on pool-0's LUN.
But the I/O was abnormal on pool-1's LUN. Extremely it looks like to be stalled.