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

  • To: xen-users@xxxxxxxxxxxxx
  • From: Gordan Bobic <gordan@xxxxxxxxxx>
  • Date: Sat, 05 Jul 2014 11:44:32 +0100
  • Delivery-date: Sat, 05 Jul 2014 10:45:02 +0000
  • List-id: Xen user discussion <xen-users.lists.xen.org>

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

ZFS send | receive is far cheaper in terms of CPU, disk I/O and network I/O than rsync.


Those guys don't use ZFS.  They must have very good reasons not to.

They do:

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:


That's the article about error rates in RAM. Disk error rates are worse.


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