Buffer I/O errors in Linux system

I have noticed these  messages in some of the linux systems . I was bit worried when I first saw them, how-ever later I came to know, these messages are harmless, “if” this system  is connected to  SAN ( ex:EMC Clariion series.) which is configured in “Active/Passive” mode and “if” the filesystem is working fine .

Jan 13 13:40:40 humble-node kernel: Buffer I/O error on device sda, logical block 0
Jan 13 13:40:40 humble-node kernel: Buffer I/O error on device sdd, logical block 0
Jan 13 13:40:40 humble-node kernel: Buffer I/O error on device sdd, logical block 1
Jan 13 13:40:40 humble-node kernel: Buffer I/O error on device sdd, logical block 2
Jan 13 13:40:40 humble-node kernel: Buffer I/O error on device sdd, logical block 3
Jan 13 13:40:40 humble-node kernel: Buffer I/O error on device sdd, logical block 4
Jan 13 13:40:40 humble-node kernel: Buffer I/O error on device sdd, logical block 5
Jan 13 13:40:40 humble-node kernel: Buffer I/O error on device sdd, logical block 6
Jan 13 13:40:40 humble-node kernel: Buffer I/O error on device sdd, logical block 7
Jan 13 13:40:40 humble-node kernel: Buffer I/O error on device sda, logical block 0

Commands like “vgscan”, “fdisk” can spit these messages .

These types of SANs contain two storage processors. LUNs are serviced through only one of the storage processors in this setup. This storage processor is called “ACTIVE”  processor..

 

The LUN can receive I/O only via Active processor. The other processor is “passive”; it acts as a backup, ready to receive I/O if the active controller fails, or if all paths to the LUN ( in multipath setup)  on the active controller fail.

Paths to the LUN going via the passive controller are passive paths and will generate  I/O errors when  I/O tried against these paths . At bootup, the kernel’s SCSI mid-layer scans all paths to find devices. Thus it will scan both active and passive paths and will generate buffer I/O errors for the passive paths. LVM can also ‘spit’ these messages ” if  proper LVM filter” is configured..

These messages can be ignored if the filesystem is working fine and you are not facing any other issues because of this, but make sure that , these messages are only reported against Passive Paths and NOT active paths..

So dont be PANIC.. 🙂