I need your help! We recently had added a second tray to our EMC VNX 5300. This one has a few SAS drives and less overall SATA space but allows the ability to fast cache, though I'm unsure how to confirm we're actively using.
Anyhow I ran a NAR as my 3rd party software is reporting high I/O. I heard back from EMC support that there are trespassed Pool LUNs, and forced flushing. Forced flushing is cause when by write cache being 100% full. This is can happen at different times on different SPs, but they can both have this problem. When write cache is 100% full, the SP will do a "forced flush" of data in write cache to the drives. While this is occurring, there will be high response times for all hosts performing writes on the CLARiiON storage system.
They offered me several articles with 50+ things it could be and rather than trying one then the other and so on wanted to see if anyone has experienced this and can offer any insight:
Software Block Version: 5.31.000.5.726
Free Raw Disk 2683.88 GB
Free Storage Pool 4169.13 GB
Used 14802.08 GB
First Enclosure 15 disk but disk 14 hot spare. 536.808 GB each RAID 5 SAS
Second Enclosure 15 disk 0 hot spare. Disk 1-4 183.44GB RAID1 SATA FLASH. Disk 5-9 536.808 GB Unbound and 10-14 RAID5 SAS.
Third Enclosure: All 536.808 with SAS RAID 5
I have 1 LUN primarily for all my data though a small one for ISO images and 1 pool with 7 Cisco UCS hosts.