Re: [Xen-users] Cheap IOMMU hardware and ECC support importance

[Gordan Bobic <gordan@xxxxxxxxxx>]

On 07/04/2014 11:45 PM, Kuba wrote:

> > > Using ZFS does not mean you don't have to do backups. File system type
> > > won't make a difference for a fire inside your enclosure:) But ZFS
> > > makes it easy to create backups by replicating your pool or datasets
> > > ("zfs send" lets you create full or incremental backups) to another
> > > set of disks or machine(s).
> > As another ZFS or as files or archives or as what?  I'm using rsync now,
> > and restoring a file is as simple as copying it from the backup.
> Typically as another ZFS dataset. Replicating ZFS snapshots has one big
> advantage for me (besides checksumming, so you know you've made your
> backup correctly) - it's atomic, so it either happens or not. It doesn't
> mean it's supposed to replace rsync, though. It depends on the task at
> hand.
ZFS send | receive is far cheaper in terms of CPU, disk I/O and network 
I/O than rsync.
> > > > > http://blog.backblaze.com/2014/01/21/what-hard-drive-should-i-buy/
> > > > Those guys don't use ZFS.  They must have very good reasons not to.
> > > They do:
> > > http://www.youtube.com/watch?v=c5ASf53v4lI
> > > http://zfsonlinux.org/docs/LUG11_ZFS_on_Linux_for_Lustre.pdf
> > >
> > > And I believe they have lots of good reasons to do so :)
> > That's some laboratory experimenting with ZFS.  Backblaze uses ext4,
> > though ZFS would seem to be a very good choice for what they're doing.
> > How can they store so much data without checksumming, without using ECC
> > RAM and not experience a significant amount of data corruption?
> That's what I found about Backblaze and ZFS (22-07-2011):
>
> We are intrigued by it, as it would replace RAID & LVM as well. But
> native ZFS is not available on Linux and we're not looking to switch to
> OpenSolaris or FreeBSD, as our current system works great for us. For
> someone starting from scratch, ZFS on one of these OSes might work and
> we would be interested to know if someone tries it. We're more likely to
> switch to btrfs in the future if anything.
That must have been written more than 3 years ago. I promise you, ZFS on 
Linux is alive and well and works great.
> > What is the actual rate of data corruption or loss prevented or
> > corrected by ZFS due to its checksumming in daily usage?
> I have experienced data corruption due to hardware failures in the past.
> Once is often enough for me and it happened more then once. If I hadn't
> done the checksumming myself, I probably wouldn't even have known about
> it. Since I started using it, ZFS detected data corruption several times
> for me (within a few years). But I don't own a data center :) Actual
> error rates might depend on your workload, hardware, probabilities and
> lots of other things. Here's something you might find interesting:
>
> http://www.zdnet.com/blog/storage/dram-error-rates-nightmare-on-dimm-street/638
That's the article about error rates in RAM. Disk error rates are worse.

Gordan


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