How to check the number of physical disks under RHEL ?
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For me this means that RHEL uses both disks as one disk only (c0d0) and installed the partitions on it.
But is there somwehere a command that tells that there are actually 2 disks in the system via CLI ?
I know that HP has an inbuild HW RAID controller, that has to be configured in the BIOS.
How can I see that HW RAID is enabled from CLI without rebooting (and watch in the BIOS) the box ?
if cat /proc/mdstat gives no output, is that sufficient to conclude that HW RAID is not active or is this command only used in Software RAID ?
That won't do it. He is asking how many "real" disks are making up the "logical" disks (LUNs) that fdisk would show as a single disk.
That is to say if you have a Hardware RAID controller that makes 4 "real" disks into a single RAID 5 "logical" disk (LUN) then in Linux fdisk would see that LUN as a single disk. It wouldn't know the underlying disk information.
It would be more complicated if you had the RAID controller doing say 1 RAID 1 (mirror) of 2 disks and another RAID 5 of 4 disks (we have this on some of our Dells with PERC controllers). That would be 6 real disks but only 2 logical disks - fdisk -l would show only 2 disks.
Off the top of my head I don't know any utility that would do this if it weren't written for the specific hardware RAID. I'm not familiar with the cciss stuff but it may be that relates to a specific driver and if so there may be utilities associated with that driver that would directly query the RAID controller to give you the information you need.
You might do it by inference:
1) Run "fdisk -l" to see how many disks Linux thinks it has and the "size" of those disks.
2) Run lspci to see what controllers/drivers are in the system - if one is for a RAID controller it might help you.
3) Guestimate RAID and number of "real disks" by knowing the size of the "real disks". e.g. if you knew you'd only installed 73 GB "real disks" and you saw a "logical" disk from fdisk -l of approximately 219 GB you could assume that you had 4 real 73 GB disks in a RAID 5 config (RAID 5 = n + 1 so your RAID 5 is "4", 4 -1 = n = 3, 3 * 73 = 219 GB)
Not an exact science to be sure.
Its even worse if its not just a controller in the host but rather an external RAID array attached via controllers. (e.g. Clariion or Symmetrix arrays attached via SAN to Qlogic fibre adapters - in that case the adapter is just passing "logical" information from the array rather than creating the array.
Most newer dl360s (g3 and above for sure) have iLO (integrated lights out monitoring) and support for the hp insight agent stuff. The insight agent will give you web access to the entire configuration of the box (memory, HDs, bios status, etc.)
Check out HP's PSP for your linux build. They typically have the insight stuff in it.