Completely unrelated to this report, one of you cache devices is dropping offline:
Apr 20 21:45:20 microserver kernel: ata6: EH complete
Apr 20 21:45:22 microserver kernel: ata6: limiting SATA link speed to 1.5 Gbps
Apr 20 21:45:22 microserver kernel: ata6.00: exception Emask 0x10 SAct 0x8000000 SErr 0x280100 action 0x6 frozen
Apr 20 21:45:22 microserver kernel: ata6.00: irq_stat 0x08000000, interface fatal error
Apr 20 21:45:22 microserver kernel: ata6: SError: { UnrecovData 10B8B BadCRC }
Apr 20 21:45:22 microserver kernel: ata6.00: failed command: READ FPDMA QUEUED
Apr 20 21:45:22 microserver kernel: ata6.00: cmd 60/00:d8:98:3e:32/01:00:01:00:00/40 tag 27 ncq dma 131072 in
Apr 20 21:45:22 microserver kernel: res 40/00:dc:98:3e:32/00:00:01:00:00/40 Emask 0x10 (ATA bus error)
Apr 20 21:45:22 microserver kernel: ata6.00: status: { DRDY }
Apr 20 21:45:22 microserver kernel: ata6: hard resetting link
Apr 20 21:45:24 microserver kernel: ata6: SATA link down (SStatus 1 SControl 310)
Apr 20 21:45:24 microserver kernel: ata6: hard resetting link
Apr 20 21:45:26 microserver kernel: ata6: SATA link down (SStatus 1 SControl 310)
Apr 20 21:45:26 microserver kernel: ata6: hard resetting link
Apr 20 21:45:29 microserver kernel: ata6: SATA link down (SStatus 1 SControl 310)
Apr 20 21:45:29 microserver kernel: ata6.00: disabled
ATA6 is MTFDDAK256MAM-1K12_1318093908F1, it wasn't even assigned at server start, but since it's part of the pool it was still being used, looks more like a cable/connection issue, see here for more info and how to better monitor the pool for errors.
If more help is needed please start a thread on the general support forum.