I have two *identical* PE R710s which will be deployed in a DRBD H/A
configuration. I plan on doing RAID5 no hotspare (redundancy relied
on at the machine level) with TWO Virtual Disks in a single disk
group.
When i create the RAID5 diskgroup with all disks and go to the
"Basic Settings" VD Size" field, i enter 80000 (MB) as i want an
~80GB Operating System volume.
I didn't look closely at the first system i configured and just
selected the remaining (automatic VDsize setting) for the second VD.
When i went to configure the second, i put in 80000MB in the VDsize
field and saw it *change* to 79999 when i went to the advanced
settings menu.
When i changed the Stripe size from 64KB to 256KB the VD Size
changed to 79996 !?. After going back and setting to 80000, then
going back to the Stripe Size widget, the VD Size went to 79997.
sigh.
After OS installation, i noted that the two machines, were in fact,
different sizes:
in1:/opt/MegaRAID # ./megacli-overview -v
[Adapter 0]
VD[0:0]=(OpSys,R(5,0,3),79996MB,#8,Optimal)
VD[0:1]=(Data,R(5,0,3),1918980MB,#8,Optimal)
in1:/opt/MegaRAID # grep . /sys/block/sd[ab]/size
/sys/block/sda/size:163831808
/sys/block/sdb/size:3930071040
in2:/opt/MegaRAID # ./megacli-overview -v
[Adapter 0]
VD[0:0]=(OpSys,R(5,0,3),79997MB,#8,Optimal)
VD[0:1]=(Data,R(5,0,3),1918976MB,#8,Optimal)
in2:/opt/MegaRAID # grep . /sys/block/sd[ab]/size
/sys/block/sda/size:163835392
/sys/block/sdb/size:3930063872
ARGH! I can understand rounding, but the fact that the VD Size
was *dynamically* changing as i selected the Advanced Settings and
Stripe Element Size menus is very disturbing. But even *that* would
be okay, *IF* both systems ended up being the same size.
# ./megacli ldinfo lall a0
on both systems shows:
# diff /tmp/foo[12]
5c5
< Size:79996MB
---
> Size:79997MB
17c17
< Size:1918980MB
---
> Size:1918976MB
Nothing else different than the fact that ONE system configured itself
to 79996MB and the other to 79997MB from my original 80000MB
specification. i.e. the stripe sizing is all the same.
('megacli adpallinfo a0' confirms no real differences in config)
Any ideas on how to ENSURE a process that gets me consistent
VD configurations?
I note that the MegaCLI user guide for 'cfgspanadd' says:
1. NOTE: Previously -szXXX expressed capacity in Mbytes but
now you can enter the capacity in your choice of units. For
example, to create a virtual drive of 10 Gbytes, enter the
size as sz10GB. If you do not enter a unit, by default it is
considered as Mbytes.
(doesn't enumerate the available UNIT types, though, but i suppose
"sectors" or "Strips" ( ;} ) wouldn't be choices)
But i'd prefer not to have to boot onto a custom live-cd in order to
carve up my RAIDs reliably, anyway.
thanks,
--stephen
--
Stephen Dowdy - Systems Administrator - NCAR/RAL
303.497.2869 - [email protected] - http://www.ral.ucar.edu/~sdowdy/
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