RAID synexeia (device sequence & grub)

[Christos Ricudis]

Nick Demou wrote:
> 2008/7/17 Haris Alatas <haris at crack.gr>:
>   
>> [...]
>> Όταν στήσεις αυτό το σύστημα να είσα σίγουρος ότι έχεις πανω καρτελάκια (στα
>> πλάγια) ποιος δίσκος είναι ποιος. Όχι το serial number και άλλα τέτοια
>> πράγματα που χρειάζονται νοημοσύνη. Απλά πράγματα: SDA , SDB, SDC
>>     
>
> ΠΡΟΣΟΧΗ! CAUTION! ACHTUNG!
>
> εδώ και κάμποσο καιρό 

"εξαπανεκαθεν" :P

> οι kernels δεν σου εγγυούνται ότι ο sda θα είναι
> πάντα sda. MONO το UUID παραμένει πάντοτε σταθερό (U for Uniq)

O SCSI Disk Driver sto linux xrhsimopoieitai peripou san generic block 
device layer - xrhsimopoieitai apo tous kainourious SATA drivers mexri 
kai tous USB mass storage drivers.  Opote sxedon otidhpote mporei na 
apo8hkeysei monimws kai randomly dedomena sto Linux, fainetai ws SCSI 
disk device. Dedomenou twra oti to assignment ginetai seiriaka - opoios 
driver kanei prwtos register ena SCSI Disk Device pairnei to minor 
device number 0, o epomenos pairnei to 1, ktl (logiko), kai dedomenou 
oti to default userland mapping metaksy device nodes kai device names 
einai epieikws gia t'ana8ema (0 = sda, 1 = sdb, ktl), h seira me thn 
opoia telika emfanizontai ta devices einai apla 8ema tyxhs. Exw spastei 
apeires fores apo to gegonos oti arkei na balw enan driver inlined ston 
kernel anti compiled san module, gia na mou allaksei OLO to sd device 
ordering.

8a mporouse kati tetoio na symmazeytei ligo me th xrhsh tou udev, alla 
den egine eks'arxhs kammia sobarh prospa8eia gia kati tetoio.

To problhma twra me ta uuids einai oti apoteloun filesystem-specific 
feature - den xarakthrizoun ena block device (to opoio synh8ws den exei 
kanena unique anagnwristiko epanw tou, me th fwteinh eksairesh twn fibre 
channel devices).

Poor man's way to detect which device is which :

mdadm --query /dev/name-of-device gia na doume an to device exei RAID 
superblock, se poio RAID set anhkei ktl
dd if=/dev/name-of-device of=/dev/null gia na doume poianou diskou to 
lampaki anabei :)