RAID controller features

Dominic Lepiane Dominic.Lepiane at
Wed Mar 3 13:47:18 CST 2010

Hi list,

We've got a bunch of different PowerEdge servers running various 
operating systems, and recently I've been banging my head against the 
wall with make some changes to the various RAIDs.

What do you guys have for feedback on what features are available from 
what RAID controllers?

For example, I have a PE2900 with a PERC 5/i.  It's got a RAID1 for OS 
plus a RAID5 for data.  I tried growing the data RAID by upgrading the 
disk sizes only to find that after much fiddling and searching Online 
that some people report the upgrade "just works" and others say "it just 
doesn't".   So fine, I've blown away the data RAID and built it anew by 
hand only silly me, I started off with a similar amount of storage first 
(fewer but larger drives) so then I had to expand the array by adding 
another disk.  Now this worked in that the array grew and OM now shows 
"2,793.00GB" but the OS (CentOS 5.4 x64) does not, it shows 1.999TB:

[root at host ~]# parted /dev/sdb p

Model: DELL PERC 5/i (scsi)
Disk /dev/sdb: 1999GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number  Start   End     Size    File system  Name  Flags
  1      17.4kB  1999GB  1999GB

Now on another server, an R710 with a PERC 6/i, I figured rather than 
get burned by a 2TB limit, I would cleverly in the RAID BIOS put 
together the RAID with multiple (sub-2TB) Virtual Disks.  That didn't 
work in the RAID BIOS and when I called Dell support thinking maybe this 
was a bug with the BIOS or some odd hardware fault, support said that 
multiple VDs on a single array wasn't "supported" though once we loaded 
an OS (Windows Server 2008) on there with OM, that was exactly the 
configuration we were able to do (two VDs on one array).

So I guess I'd like to know if Dell offers any products that have the 
following features and under what configurations they work:

1) Array expansion by replacing smaller disks with larger ones
2) Arrays over 2TB in size
3) Carving of arrays into multiple VDs (or auto-carving any arrays into 
2TB and smaller VDs)
4) More sophisticated operations like dropping disks from arrays where 
not all array space is used by VDs

I'd definitely like to know about internal storage like PERC or those 
H200/H700 (I haven't used any of these yet), but I'd also like to hear 
your feedback on direct attached (MD1000 etc) or SAN (Equilogic? )

- Dominic

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