Question Regarding Value of Snapshots in My Set Up

[benthomas]

Hi all,

Very new to FreeNAS but growing to love it as I learn more about it. I have recently replaced my Thecus N5200 NAS which I had set up in RAID5 (2.7Tb total storage) with the following:

HP Microserver N36L - bought a few when they were dirt cheap (set the others up for friends using WHS, work a treat).
8Gb RAM
5 x 2Tb Seagate Barracuda Green 5900rpm HDD, I have a nicely fitting caddy in the optical bay and are using the hacked firmware to get the full speed on that SATA port.
Intel 1Gb CT PCIe NIC
Corsair Flash Voyager Mini 4Gb for FreeNAS in internal USB port
FreeNAS-8.0.3-RELEASE-p1-x64 (9591)

I have created a ZFS volume using all 5 disks in RAID-Z and I've created a ZFS dataset for each of the CIFS shares that I wanted. I did it this way after reading the advice in the documentation.
The purpose of this unit is as a home file/media server.

Everything has run very smoothly with the set up and I have transferred all my files across from the old NAS. I am already impressed with the transfer speeds and I reckon on average it's twice as fast as the N5200. I'm not sure how it compares to others but from my W7 machine I can copy 2Gb of mixed file sizes in just under 2 minutes. Copy speed varies significantly during the process from under 1Mb/s to up to 105Mb/s. I'm not sure why it does this, it seems to transfer the large files very quickly and the smaller ones very slowly. Transfers to the N5200 seem to have a very steady, consistent speed but it was probably a little sluggish at around 15-20Mb/s. Either way, I'm pretty happy with the speed overall of my new FreeNAS server. Also, I have followed the tips I found here and other places in relation to improving CIFS performance via the settings.

My question is (unrelated to the transfer speeds but welcome comment on that anyway), would the snapshot function be worthwhile in my circumstances? As I understand it I have one disk redundancy and my valuable data I also back up online nightly (over kill but it doesn't hurt). I don't have or need off-site replication. The only value of snapshots that I can see would be for accidental deletion or a historical record of file changes. Knowing this, does anyone see any major value in having local snapshots?

Thanks for your help in advance. If there is any more info I need to include to help you assist please let me know.

Cheers.

 

[xbmcg]

It's like a time-machine. You can always access any file back in time, as long as the snapshot is there (with almost no additional cost for space). This is a great feature, if you accidently kill some files or modify them and want to revert your changes.

The zfs actually keeps all unchanged sectors and replace only the changed with new one and chain them into the file. The old remain untouched and the old alternative chain remains as "snapshot". Old snapshots are automaticaly removed on a schedule base, so just set it and forget it until you need to recover some old state. Just amazing. This is one of the bigest advantages over classic raid - beside zfs' huge address range and checksum per sector security.

 

[benthomas]

That's great, thank you. Is it fair to say there wouldn't be much point including my movies/TV shows etc as part of the snapshots? Is it more relevant to personal files etc.?
Cheers.

 

[William Grzybowski]

Yes, you usually want snapshots over dir/files that change over time and would be important to rollback to a certain point in time... e.g. before you accidentally delete your super important family photos, docs, etc.

 

[digitaltrash]

"[...] it seems to transfer the large files very quickly and the smaller ones very slowly."

This has to do with IOPS that your disks (and system) can handle. See this article

 

[xbmcg]

It can be useful even on video data / movies - e.g. you try a new media manager, thar changes / adds conten to your file system or accidently deletes or modifies files (on music data e.g.mp3 tag information, nfo files, fanart, thumbs etc.) and screws up your data. You can just go back to the last known good snapshot. whithout the need to have a backup tape somewhere or to fix / revert all changes manually....