Hi Juhani,
First, this is the reason why you should not use RAID0, if a single drive goes down, so does the Volume. Please use RAID5.
If it was the top drive, aka PD1, then the way to bring your Volume online is as follows.
promise@promises-Mac-mini ~ % promiseutil
-------------------------------------------------------------
Promise Utility
Version: 4.06.0000.01 Build Date: Aug 4, 2021
-------------------------------------------------------------
List available RAID HBAs and Subsystems
===============================================================================
Type # Model Alias WWN Seq
===============================================================================
hba 1 * Pegasus M4 2000-0001-5564-6efc 1
Totally 1 HBA(s) and 0 Subsystem(s)
-------------------------------------------------------------
The row with '*' sign refers the current working HBA/Subsystem path
To change the current HBA/Subsystem path, you may use the following command:
spath -a chgpath -t hba|subsys -p <path #>.
Type help or ? to display all the available commands
-------------------------------------------------------------
cliib> logdrv
===============================================================================
LdId Alias OpStatus Capacity Stripe RAID CachePolicy SYNCed
===============================================================================
0 Offline 8.19TB 1MB RAID0 RAhead/WBack Yes
cliib> phydrv -a online -p 1
cliib> logdrv
===============================================================================
LdId Alias OpStatus Capacity Stripe RAID CachePolicy SYNCed
===============================================================================
0 OK 8.19TB 1MB RAID0 RAhead/WBack Yes
cliib>
That is, open a terrminal, enter promiseutil, then use the command
phydrv -a online -p 1
The logdrv commands are to show the status.