[clug-talk] WD Green HDD's with ZFS

Andrew J. Kopciuch akopciuch at bddf.ca
Sun Mar 25 21:26:09 PDT 2012


On March 25, 2012, Royce Souther wrote:
> I have a few file servers that I am using Western Digiatl Green HDD's with
> LVM. I am not using RAID1 because that would burn out a Green drive very
> quickly. My servers are identical clones of each other and I like that
> better then RAID1 because if a power supply dies the other server keeps the
> work going until I can get the dead one fixed.
>

I'm not sure what you mean by "burn out".  It depends on the actual drives, 
but as I understand it, the draw back from using the WD drives is they do not 
have TLER.  That can cause stability (ie. performance degradation) if you 
have a nice RAID controller, as it will mark the drive(s) as unreliable 
because they are not responsive while fixing read/write errors themselves.  
That's only when you have read/write errors ... it's not all the time.

> I one big issue with LVM is having to unmount the file system to resize the
> partition. Every time I add a drive and grow the system it takes longer and
> longer to go through the steps of fsck'ing the partiion and then resizing
> it. It takes most of a day now to do this. ZFS does not have this problem.
> As I understand it ZFS is able to resize the file system on the fly.
> Mirrored Vdev would be like using RAID1 and that would kill a Green drive
> but just using a ZFS to have the abilty to grow the FS on the file would be
> good enough and should not hurt the Green drives. Does anyone know if using
> ZFS not using mirror would be safe to use on drives like these?

Your gripe is with your filesystem not LVM.

You might not need to unmount the filesystem to resize it.  It depends on a 
lot of things.

XFS & JFS filesystems _have_ to be mounted in order to resize actually.   
reiserfs can be either or.   For ext filesystems it depends on on the 
versions, kernel, and kernel options you have.  The utility you want is 
ext2online.   

You extend the underlying volume the filesystem is on with lvextend, and then 
extend the filesystem with ext2online.   e2fsadm apparently will do both of 
those steps in one shot for you.  There are some incompatibility issues 
between LVM1 & LVM2 utilities apparently

I've never used ZFS, but it's apparently all-in-one.  Manage devices, volumes, 
partitions, FS ... all from the command line with the utilities.

--

If you have brand new servers (meaning not deployed).   I'd create your 
volumes, and use XFS on top of the volume.  You can "convert" the filesystem 
if already deployed, but that seems risky to me ... but should be possible.


Andy
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