LinuxQuestions.org - strange HDD problem

Hello, guys.

I've been seeing the following errors at all of my servers since the last Wednesday.

Code:

ata2.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0

ata2.00: (irq_stat 0x40000001)

ata2.00: cmd b0/d5:01:09:4f:c2/00:00:00:00:00/00 tag 0 cdb 0x0 data 512 in

res 51/04:05:b3:4f:c2/00:00:00:00:00/00 Emask 0x1 (device error)

ata2.00: configured for UDMA/133

ata2: EH complete

SCSI device sdb: 976773168 512-byte hdwr sectors (500108 MB)

SCSI device sdb: drive cache: write back

The problem is found only at the servers that have Western Digital HDDs installed (different WD models).
One of the servers has Seagate and WD HDDs and I see errors only regarding WD at the log.

Also there is no any SMART error at WD:

Code:

SMART Self-test log structure revision number 1

Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error

# 1  Extended offline    Completed without error      00%      1340        -

What's the problem with it?
All of the servers were working correctly until the last Wednesday...