Persistent boot disks issue

Hi all,
please i need your help urgently

I am faced to a serious boot disks issue on an Sun Fire E2900.
The system run with two disque in zpool .
The operating system is Solaris 10 (ZFS)

The first time the issue occured, i got the error below on the two disks:

[ Apr 7 08:04:33 sdp032 scsi: [ID 107833 kern.warning] WARNING: /ssm@0,0/pci@18,700000/scsi@2 (mpt0):
Apr 7 08:04:33 sdp032 Target 0 reducing sync. transfer rate
Apr 7 08:04:33 sdp032 mpt: [ID 795936 kern.warning] WARNING: ID[SUNWpd.mpt.sync_wide_backoff.6014]
Apr 7 08:04:33 sdp032 scsi: [ID 107833 kern.warning] WARNING: /ssm@0,0/pci@18,700000/scsi@2/sd@0,0 (sd5):
Apr 7 08:04:33 sdp032 Error for Command: write(10) Error Level: Retryable
Apr 7 08:04:33 sdp032 scsi: [ID 107833 kern.notice] Requested Block: 239904668 Error Block: 239904668
Apr 7 08:04:33 sdp032 scsi: [ID 107833 kern.notice] Vendor: FUJITSU Serial Number: 0613C07UL4
Apr 7 08:04:33 sdp032 scsi: [ID 107833 kern.notice] Sense Key: Aborted Command
Apr 7 08:04:33 sdp032 scsi: [ID 107833 kern.notice] ASC: 0x47 (scsi parity error), ASCQ: 0x0, FRU: 0x0
Apr 7 08:04:33 sdp032 scsi: [ID 107833 kern.warning] WARNING: /ssm@0,0/pci@18,700000/scsi@2 (mpt0):
Apr 7 08:04:33 sdp032 Target 1 reducing sync. transfer rate
Apr 7 08:04:33 sdp032 mpt: [ID 795936 kern.warning] WARNING: ID[SUNWpd.mpt.sync_wide_backoff.6014]
Apr 7 08:04:33 sdp032 scsi: [ID 107833 kern.warning] WARNING: /ssm@0,0/pci@18,700000/scsi@2/sd@1,0 (sd6):
Apr 7 08:04:33 sdp032 Error for Command: write(10) Error Level: Retryable
Apr 7 08:04:33 sdp032 scsi: [ID 107833 kern.notice] Requested Block: 239904668 Error Block: 239904668
Apr 7 08:04:33 sdp032 scsi: [ID 107833 kern.notice] Vendor: FUJITSU Serial Number: 0648C0ABE4
Apr 7 08:04:33 sdp032 scsi: [ID 107833 kern.notice] Sense Key: Aborted Command
Apr 7 08:04:33 sdp032 scsi: [ID 107833 kern.notice] ASC: 0x47 (scsi parity error), ASCQ: 0x0, FRU: 0x0]

The two disks have been replaced and we restored the the pool.

After one month, i got firmware error below and we can't connect to the server throught ssh:
[ Apr 3 10:00:24 sdp032 scsi: WARNING: /ssm@0,0/pci@18,700000/scsi@2 (mpt0):
Apr 3 10:00:24 sdp032 firmware image bad or mpt ARM disabled. Cannot attempt to recover via firmware download because driver's stored firmware is incompatible with this adapter.
Apr 3 10:00:24 sdp032 scsi: WARNING: /ssm@0,0/pci@18,700000/scsi@2 (mpt0):
Apr 3 10:00:24 sdp032 mpt restart ioc failed
Apr 3 10:00:24 sdp032 scsi: WARNING: /ssm@0,0/pci@18,700000/scsi@2,1 (mpt1):
Apr 3 10:00:24 sdp032 firmware image bad or mpt ARM disabled. Cannot attempt to recover via firmware download because driver's stored firmware is incompatible with this adapter.]

I upgrade the server's firmware to the latest version 5.20.16

5 days later, we got same firmware error and we replace again the two disks and the system has been restored but the problem was not solve .

Now we have again the same disks error again.

[ Apr 10 03:09:46 sdp032 scsi: [ID 107833 kern.warning] WARNING: /ssm@0,0/pci@18,700000/scsi@2 (mpt0):
Apr 10 03:09:46 sdp032 Target 0 reducing sync. transfer rate
Apr 10 03:09:46 sdp032 mpt: [ID 795936 kern.warning] WARNING: ID[SUNWpd.mpt.sync_wide_backoff.6014]
Apr 10 03:09:46 sdp032 scsi: [ID 107833 kern.warning] WARNING: /ssm@0,0/pci@18,700000/scsi@2/sd@0,0 (sd5):
Apr 10 03:09:46 sdp032 Error for Command: read(10) Error Level: Retryable
Apr 10 03:09:46 sdp032 scsi: [ID 107833 kern.notice] Requested Block: 127026944 Error Block: 127026944
Apr 10 03:09:46 sdp032 scsi: [ID 107833 kern.notice] Vendor: FUJITSU Serial Number: 0613C07UL4
Apr 10 03:09:46 sdp032 scsi: [ID 107833 kern.notice] Sense Key: Aborted Command
]