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I know ZFS is usually used for numerous reasons including it's amazing mirroring features. However in this instance the machine I've been tasked with setting up has a RAID-1 setup so I only have one logical disk.

My reason for wanting ZFS is primarily that of snapshots - is this the right tool for the job or is there a better way to efficiently emulate ZFS snapshot?

I'm having a chicken or egg problem - is it possible to install a base RHEL system with one disk (/dev/sda) using ZFS? It seems all references I can find use it to pool numerous disks with the base system not being mentioned. How would I achieve this?

Please let me know if I can clarify this at all as I'm fully aware my explanation is lackluster at best.

share|improve this question
I hadn't considered BTRFS for this however it may suit my needs as well. – WinkyWolly May 23 '13 at 19:05
I do this with ZFS often... I'll write more detail later. However, can you give me some idea of how you plan to use the snapshots? – ewwhite May 23 '13 at 19:09
It's primarily for an integrity / security standpoint. This will be a low resource system (IO, CPU). I intend on 12-24 hour snapshots in case there is a breach so we could fall back on a known secure version. Relatively simple use case that I may be over-thinking. – WinkyWolly May 23 '13 at 19:16
Btrfs still isn't there, and unless you abandon the RHEL kernel for a newer Kernel you are stuck with the version of Btrfs which was shipped with RHEL, you'll be using an older version of Btrfs and the Btrfs-utils which is already obsolete. – Stefan Lasiewski May 23 '13 at 21:40
_ is this the right tool for the job_ -- This depends on what you want to do with the snapshots. What are you trying to accomplish with the snapshots? – Stefan Lasiewski May 23 '13 at 21:42

I'll answer. You may be overthinking...

Snapshots aren't backups. So if you're trying to protect against a compromise, you should go the extra step and back up to another device. Now, snapshots can be extremely helpful in producing a clean consistent copy of your data to ship or back up to another device.

As far as ZFS on Linux, It's very easy to integrate into existing RHEL installs. I only use ZFS on data partitions, though. If I have a Linux system, I boot using the normal default filesystems. In the example below, on the /data partition is a ZFS filesystem. That way, I can snapshot or apply granular settings (compression in this case) where they're needed.

[root@MDMarra ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/cciss/c0d0p2      12G  2.4G  8.9G  22% /
tmpfs                 7.8G  4.0K  7.8G   1% /dev/shm
/dev/cciss/c0d0p1     291M   59M  218M  22% /boot
/dev/cciss/c0d0p7     2.0G  119M  1.8G   7% /tmp
/dev/cciss/c0d0p3     9.9G  1.9G  7.5G  21% /usr
/dev/cciss/c0d0p6     6.0G  318M  5.3G   6% /var
vol1/data             118G   55G   63G  47% /data

If you just need the ability to create a block device snapshot at any time, Idera Hot Copy can do the job. These snapshots won't persist across reboots, though.

share|improve this answer
I was overthinking this initially and answered my own question. We use Idera heavily however I more of wanted a read-only snapshot in case of a compromise so it'd be easy to quickly roll back while investigating (and seeing exactly when it happened). The benefit of rolling out snapshots to new nodes was highly favorable too (zfs send, zfs receive). I think I'm scrapping the idea of ZFS currently however because I have a single disk and it'd be a single partition in the pool - hardly taking advantage of the positives of ZFS (unless I'm mistaken). Thank you for the reply. – WinkyWolly May 24 '13 at 2:44
There's nothing wrong with using single-disk or single-volume ZFS. I make use of ZFS for compression and often present RAID volumes to it. This is fine. – ewwhite May 24 '13 at 9:42

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