Thanks kenatonline! I should thought about Debian in the first place.
But I have faced another disk problem with Debian.
All the steps up to "Partition disks" go fine.
The step partition disks show a funny window "this is an overview...." with only two options - "undo changes" and "finish partitioning"... but I did nothing to partition the disks!
The result is predictable - "finish" leads to an error message - "no root defined", "undo" - just hands... well, it is not an expected, but anyway.
Am I doing something wrong yet again?
Also I have noticed after NAS boots the Squeeze kernel it shuts down disks (or put them into a power saving mode). Is it an expected behaviour?
the dmesg fragment
[ 3.130482] sata_mv sata_mv.0: version 1.28
[ 3.141679] sata_mv sata_mv.0: slots 32 ports 2
[ 3.167739] scsi0 : sata_mv
[ 3.182345] scsi1 : sata_mv
[ 3.193761] ata1: SATA max UDMA/133 irq 29
[ 3.197992] ata2: SATA max UDMA/133 irq 29
[ 3.555904] ata1: SATA link down (SStatus 0 SControl 300)
[ 3.905912] ata2: SATA link down (SStatus 0 SControl 300)