[BBLISA] RE: storevault / netapp

[Peter Galvin]

RAID can be implemented in hardware or software. Can't speak to all hardware
RAID controllers, but NetApp does RAIDDP, and ZFS has RAIDZ2, both of which
are double-parity-disk RAID (i.e. Survive 2 disk failures rather than 1).

At the moment ZFS cannot expand a storage pool by single disk increments.
You could for example expand a RAIDZ pool by concatenating another RAIDZ set
to it, but not by adding a single disk.


On 2/27/08 11:44 AM, "Edward Ned Harvey" <bblisa2 at nedharvey.com> wrote:

>>> I know you can get snapshotting from sun, but can you do
>>> dualparity or expand on the fly?
>> 
>> Absolutely.  ZFS.  That is what we are moving everything to.
> 
> The first one, snapshotting, I am fully convinced, is awesomely supported in
> solaris with ZFS.
> 
> The second one, what I'm referring to as "dualparity" is the ability to
> sustain 2 simultaneous disk failures without data loss.  This is a function
> of the hardware raid controller, and not the filesystem.  Am I making any
> bad assumptions here?  I am not aware of any hardware raid controllers that
> can safely lose two disks at the same time, except the
> netapp/storevault/other enterprise filers.  What I'm saying is, it's not
> supported like this on a sun xstore solaris zfs machine.  Right?
> 
> What I'm referring to as "volume expansion on the fly" is the ability to
> incrementally add disks, without degradation of redundancy or downtime.  If
> I've got 6 disks in a dualparity configuration, controlled by hardware DP
> raid (usable capacity of 4 disks assuming no hotspare), I just slap in one
> more disk, and increase the size of my FS by 25%.  No downtime, no
> degradation of redundancy.  Perhaps the system runs slow for a couple hours.
> This too is not supported in the sun xstore solaris zfs configuration,
> right?
> 
> 
>> Try some xstore's with Solaris 10 + ZFS (x86 of course), we buy
>> large batches of SAS 1TB spindles for around $280 and build them
>> ourselves.  ZFS is also now available on FreeBSD, Linux, and even Mac
>> OSX
>> if you have an aversion to Solaris
> 
> As it happens, I have no aversion to solaris.  It's pretty darn good.  And
> since I learned ZFS supports this snapshotting, I've been browsing around
> and looking at ZFS all around.
> 
> I don't think it's fair to say it's supported in OSX.  In OSX, you cannot
> format and create a ZFS filesystem, and you can only mount it read-only.
> Although read/write variations exist, they are very immature at best.
> 
> Same is true for Linux.  Although it's open source, it can't be compiled in
> the linux kernel any time soon.  Because it's written under CDDL, which
> conflicts with GPL.  See here:  http://en.wikipedia.org/wiki/ZFS#Platforms
> 
> 
> 
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--Peter

Blog: http://pbgalvin.wordpress.com