LVM, usb drives, Active Directory

[dsr-mzpnVDyJpH4k7aNtvndDlA at public.gmane.org (Dan Ritter)]

On Tue, Dec 15, 2009 at 07:49:32AM -0500, Scott Ehrlich wrote:
> I have a client with a handful of USB drives connected to a CentOS
> box. ? I am charged with binding the USB drives together into a single
> LVM for a cheap storage data pool (10 x 1 TB usb drives = 10 TB cheap
> storage in a single mount point).

= very likely to be unusable.

Let's suppose you expect a drive to die once in four years, on
average, at which point you will replace it. 

For a ten-disk filesystem as you have outlined, you can expect
downtime and loss of data every 5 months or so.

USB tends to be fragile over the long run, too. In my
experience, you can assume that a USB-connected disk will need a
bus reset every 6-8 weeks. If it's part of an LVM filesystem as
above, that's another downtime + potential loss of data event.

If you want to have a 10 TB filesystem which has reliability as
the first goal, and cheapness as the second, I would move the
disks into (e)SATA enclosures, which will solve the USB
flakiness problem, and get more of them, to do Linux software
RAID. Best would be RAID10 with 20 disks, although overall it
may be cheaper to do RAID10 with 10 2TB disks. If you really
have to go cheap, RAID6 with 7 2TB disks.

Or.

Do you really need to present a 10 TB filesystem, or is it just
for convenience in mounting? I believe you could offer an export
of /storage, and have the machine with all the disks mount them
on /storage/1, /storage/2, etc. That way you don't do RAID or
LVM concatenation at all, and you don't get the ability to store
 >1TB files, but you do get loss isolation -- if /storage/4 goes
down, you only have to recover that 1 TB volume and the rest of
the filesystems are still available.

> The next fun piece is how to incorporate that storage space into an
> existing Active Directory structure to apply AD acls for limited
> access.
> 
> I'd rather not use Samba, as that is its own infrastructure and
> maintains its own credentials database.

I don't know enough to answer this definitively, but I'm pretty
sure that Samba is the right system for people looking to
integrate Windows filesharing and AD.

-dsr-

-- 
http://tao.merseine.nu/~dsr/eula.html is hereby incorporated by reference.
You can't defend freedom by getting rid of it.