[CentOS] Lost raid when server reboots

carlopmart carlopmart at gmail.com
Wed Nov 11 15:27:40 UTC 2009

Ross Walker wrote:
> On Nov 11, 2009, at 9:33 AM, "nate" <centos at linuxpowered.net> wrote:
>> carlopmart wrote:
>>> Hi all,
>>>  I have setup a raid1 between two iscsi disks
>> Why would you think to attempt this? iSCSI is slow enough as
>> it is, layering RAID on top of it would be even worse. Run RAID
>> on the remote iSCSI system and don't try to do RAID between
>> two networked iSCSI volumes, it will hurt performance even more.
> I think the OP was thinking storage subsystem redundancy. It's not  
> that bad of an idea since Linux RAID1 uses bitmaps for changed blocks  
> so the whole RAID1 doesn't have to be resilvered on a disconnect.
> ISCSI isn't that slow, I have found that it is only limiting for  
> extremely high bandwidth applications, but there is 10Gbe for those.
>>>  Why md0 is not activated when I reboot this server? How can I do  
>>> this
>>> persistent
>>> between reboots??
>> Probably because the iSCSI sessions are not established when the
>> software raid stuff kicks in. You must manually start the RAID
>> volume after the iSCSI sessions are established.
> True, and I believe there is a initrd option for iSCSI devices at boot  
> that one can set in /etc/sysconfig/initrd if you apropos/grep/google  
> I'm sure you will find it. It's for iSCSI boot devices.
>> The exception would be if you were using a hardware iSCSI HBA
>> in which case the devices wouldn't show up as iSCSI volumes they
>> would show up as SCSI volumes and be available immediately upon
>> booting, as the HBA would handle session management.
> True HW iSCSI would make sure they were available at boot, but CentOS  
> has had iSCSI boot device support since 5.1 one just needs the module  
> and tools in the initrd and there is an option for that.
> -Ross

Thanks to all. i have reconfigured initrd to use iscsi disks and all works well.

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CL Martinez
carlopmart {at} gmail {d0t} com

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