[CentOS] blocks 256k chunks on RAID 1

Hi, I have a RAID 1 (using mdadm) on CentOS Linux and in /proc/mdstat I see this:

md7 : active raid1 sda2[0] sdb2[1] 26627648 blocks [2/2] [UU] [-->> it's OK] md1 : active raid1 sdb3[1] sda3[0] 4192896 blocks [2/2] [UU] [-->> it's OK] md2 : active raid1 sda5[0] sdb5[1] 4192832 blocks [2/2] [UU] [-->> it's OK] md3 : active raid1 sdb6[1] sda6[0] 4192832 blocks [2/2] [UU] [-->> it's OK] md4 : active raid1 sdb7[1] sda7[0] 4192832 blocks [2/2] [UU] [-->> it's OK] md5 : active raid0 sdb8[1] sda8[0] 8385536 blocks 256k chunks [-->>>>>> What's the meaning of this? Is it an error on the hdds? What can I do to fix this?]

Thanks in advance.

regards, Israel