[CentOS] Re: CentOS 5 Dual Drive Confusion

Scott Silva ssilva at sgvwater.com
Mon Apr 2 16:03:05 UTC 2007


Brett Serkez spake the following on 4/1/2007 3:04 PM:
> I performed a test install of CentOS Beta 5 on a system with two ~60
> GB drives.  When installing CentOS 4 on this system, I normally work
> thru setting up Software RAID with identically sized partitions on
> each drive.
> 
> For my test, the CentOS installer only presented a single drive.  I
> took the default of letting it do what it wanted.  After looking over
> the system I have verified that /boot is using DMRAID, but it isn't
> not clear if the balance of the drive for the root file system is
> using both drives or not, I think it might be.
> 
> Using fdisk, I can see both disks are carved out identically:
> 
>   Device Boot      Start         End      Blocks   Id  System
> /dev/hda1   *           1          13      104391   83  Linux
> /dev/hda2              14        7297    58508730   8e  Linux LVM
> 
> /dev/hdd1   *           1          13      104391   83  Linux
> /dev/hdd2              14        7297    58508730   8e  Linux LVM
> 
> Using dmraid it *looks* like the drives are mirrored in total?
> 
> dmraid -r -D
> /dev/hda: pdc, "pdc_bacfgfjaf", mirror, ok, 117231345 sectors, data@ 0
> /dev/hdd: pdc, "pdc_bacfgfjaf", mirror, ok, 117231345 sectors, data@ 0
> 
> But then using df it is less obvious:
> 
> df -h
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/mapper/VolGroup00-LogVol00    54G 1009M   50G   2% /
> /dev/mapper/pdc_bacfgfjafp1             99M   11M   83M  12% /boot
> tmpfs                 125M     0  125M   0% /dev/shm
> 
> pvs shows VolGroup00 as using pdc_bacfgfjafp2:
> 
> PV                          VG         Fmt  Attr PSize  PFree
>  /dev/mapper/pdc_bacfgfjafp2 VolGroup00 lvm2 a-   55.78G 32.00M
> 
> which is RAID1??????
> 
> Seems to be:
> 
> dmraid -s
> *** Active Set
> name   : pdc_bacfgfjaf
> size   : 117231232
> stride : 128
> type   : mirror
> status : ok
> subsets: 0
> devs   : 2
> spares : 0
> 
> Am I properly understanding that by default, CentOS 5 is creating a
> full drive mirrored RAID?  Then for other than the boot partition, it
> is laying LVM over this mirrored RAID, presumably to allow adjustments
> later?
> 
> Thank you in advance,
> 
> Brett
Does the board have an onboard fakeraid? I think that is what DMRAID does. It
supports some of the fakeraid controllers, although it is much less mature
than plain software raid.


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