We do this: we have, connected to an amd64 server via a QLogic
QLA-2340 to an FC switch, several RAID devices (XServe RAID, Nexsan
SATABeast) totalling 15 PVs in a single 27TB VG, with various XFS
filesystems, several of which approach 8-10TB. These filesystems are
then exported to a small lab of NFS clients. The vgdisplay:
--- Volume group ---
VG Name Storage2
System ID
Format lvm2
Metadata Areas 15
Metadata Sequence No 39
VG Access read/write
VG Status resizable
MAX LV 256
Cur LV 8
Open LV 7
Max PV 256
Cur PV 15
Act PV 15
VG Size 27.74 TB
PE Size 32.00 MB
Total PE 909076
Alloc PE / Size 905658 / 27.64 TB
Free PE / Size 3418 / 106.81 GB
I'm only mostly (rather than completely) convinced of the
righteousness of this approach, but it's been working for us, give or
take a dramatic episode that we never managed to completely diagnose
(the SCSI layer blew up in a way that acted like a hardware failure,
but with ultimately no clear evidence that the heart of the fault
wasn't an XFS corruption and no real device problem). We have lost
and replaced drives in the RAID arrays, though it is a little heart-
stopping.
We're doing no meaningful fail-over, other than having a second
server configured and ready to replace the primary one in the case of
server catastrophe (which has happened). No multipathing, no
clustering.
Any commentary on the appropriateness of this approach? Occasionally
I look over at ZFS and the way it collapses the software stack to a
single component, and get a little jealous...
Regards,
Andy Boyko andy@boyko.net
On Sep 20, 2006, at 10:48 AM, Alexander Lazarevich wrote:
I should have been more clear. I'm not worried about LVM on one
RAID. My questions is specifically about creating an LVM volume
group ACROSS two RAID's.
For example, we have a 64bit linux server, with two different RAID
devices attached to the host via Fiber. These RAID's are each 4TB
volumes. The RAID is attached as /dev/sda and /dev/sdb. What I'm
asking about is creating a LVM volume group, and joining /dev/sda
AND /dev/sdb to that same volume group, creating the lv of 8TB
(minus overhead of course), and then creating a filesystem on that
lv. A 8TB filesystem, which is spanned (via LVM) across both RAID's.
Does anyone here do that? Reading all the reply's I realize I
wasn't clear enough about that, and neither was anyone's responses.
Alex
On Wed, 20 Sep 2006, Matthew B. Brookover wrote:
I have used LVM on top of software raid and ISCSI. It works
well. It
also helps keep track of what device is where. ISCSI does not export
its targets in the same order, some times sdb shows up as
sdc.... LVM
will keep track of what is what.
Matt
On Tue, 2006-09-19 at 16:53 -0500, Alexander Lazarevich wrote:
We have several RAID devices (16-24 drive Fiber/SCSI attached
RAID) which
are currently single devices on our 64bit linux servers (RHEL-4,
core5).
We are considering LVM'ing 2 or more of the RAID's into a LVM
group. I
don't doubt the reliability and robustness of LVM2 on single
drives, but I
worry about it on top of RAID devices.
Does anyone have any experience with LVM on to of RAID volumes,
positive
or negative?
Thanks,
Alex
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