FAQ
Hello,

I have a Promise EX 12-port RAID controller in my box, connected to 8
750GB disks. I have set up 2 RAID-5 devices and joined these using LVM.

This is working fine.

However, there is something that seems wrong..
(4-1) * 750 = 2250, but df reports the LVM volume as a mere 4.0T;

/dev/mapper/storage_volume-stor 4.0T 3.6T 507G 88% /storage

Shouldn't this be 4.5TB?


Relevant bit of boot log:

scsi4 : stex
Vendor: Promise Model: 4 Disk RAID5 Rev: 1.10
Type: Direct-Access ANSI SCSI revision: 02
sdb : very big device. try to use READ CAPACITY(16).
SCSI device sdb: 4395053952 512-byte hdwr sectors (2250268 MB)
sdb: Write Protect is off
sdb: Mode Sense: 00 12 00 00
SCSI device sdb: drive cache: write back
sdb : very big device. try to use READ CAPACITY(16).
SCSI device sdb: 4395053952 512-byte hdwr sectors (2250268 MB)
sdb: Write Protect is off
sdb: Mode Sense: 00 12 00 00
SCSI device sdb: drive cache: write back
sdb: sdb1
sd 4:0:0:0: Attached scsi disk sdb
sd 4:0:0:0: Attached scsi generic sg1 type 0
Vendor: Promise Model: 4 Disk RAID5 Rev: 1.10
Type: Direct-Access ANSI SCSI revision: 02
sdc : very big device. try to use READ CAPACITY(16).
SCSI device sdc: 4395053952 512-byte hdwr sectors (2250268 MB)
sdc: Write Protect is off
sdc: Mode Sense: 00 12 00 00
SCSI device sdc: drive cache: write back
sdc : very big device. try to use READ CAPACITY(16).
SCSI device sdc: 4395053952 512-byte hdwr sectors (2250268 MB)
sdc: Write Protect is off
sdc: Mode Sense: 00 12 00 00
SCSI device sdc: drive cache: write back
sdc: sdc1
sd 4:0:4:0: Attached scsi disk sdc
sd 4:0:4:0: Attached scsi generic sg2 type 0
Vendor: Promise Model: RAID Console Rev: 1.00
Type: Processor ANSI SCSI revision: 03
scsi 4:0:16:0: Attached scsi generic sg3 type 3

--
Cheers,
Morten
:wq

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  • Tim Verhoeven at Mar 29, 2008 at 1:03 pm

    On Sat, Mar 29, 2008 at 12:45 PM, Morten Nilsen wrote:
    Hello,

    I have a Promise EX 12-port RAID controller in my box, connected to 8
    750GB disks. I have set up 2 RAID-5 devices and joined these using LVM.

    This is working fine.

    However, there is something that seems wrong..
    (4-1) * 750 = 2250, but df reports the LVM volume as a mere 4.0T;

    /dev/mapper/storage_volume-stor 4.0T 3.6T 507G 88% /storage

    Shouldn't this be 4.5TB?
    No, because storage vendors count in decimal, 750 GB is 750000000000
    bytes instead of 805306368000 if you count binary.

    So 750 decimal GB is is actually 698 binary GB. And 8 disks in 2 RAID
    5 arrays is (6 * 698)/1024 = 4,09 TB (binary).

    So it is ok, you did not loose any storage.

    Regards,
    Tim

    --
    Tim Verhoeven - tim.verhoeven.be@gmail.com - 0479 / 88 11 83

    Hoping the problem magically goes away by ignoring it is the
    "microsoft approach to programming" and should never be allowed.
    (Linus Torvalds)
  • Kai Schaetzl at Mar 29, 2008 at 1:31 pm

    Morten Nilsen wrote on Sat, 29 Mar 2008 12:45:02 +0100:

    750GB
    vendors use 1.000 instead of 1.024 for these figures. The difference
    wasn't much with the small disks some years ago, but with over 100 Gig
    disks it means you "loose" a good amount of space.

    Kai

    --
    Kai Sch?tzl, Berlin, Germany
    Get your web at Conactive Internet Services: http://www.conactive.com

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