Sunday, October 18, 2015

Replacing a Time Capsule with a Synology NAS - Time Machine for multiple machines

When my first Time Capsule died young I grumbled and bought another. When the second Time Capsule died even younger I decided to try a Synology NAS [1]. If nothing else, maybe restores would, maybe, actually work.

Yes, Apple’s Time Capsule sucks. So does Apple to be honest. But you go to war with the army you have ...

Synology has a technical article on configuring Time Machine, but it assumes you have only one Mac.That’s dumb. If I had only one Mac I’d use an external drive cradle.

Two web sites were particularly helpful

To begin with I purchased a consumer grade Synology DS215j for $200 . This device is widely used and has a good reputation, but I suspect it’s due for replacement soon. I like using old stable stuff so this was fine with me. I bought it through Amazon where it was clear most users buy a pair of WD Red 4TB NAS drive to go with it. Installation was simple — but I still got confused! Synology provides two sets of screws, one for the drive mount and the other for case closure. They also provide extra screws for each! So, of course, I ended up thinking the packet of 10 screws was 8 mounts and 2 case. Except they don’t fit the case… Ok. Look for the other wee packet.
So far my Synology setup seems fairly quiet. If you hear a loud fan noise you probably got a bum unit (OTOH I expect the fan will get loud in a year or two.)
The initial setup defaults to Synology’s version of RAID 1 Synology Hybrid Raid (SHR). Use the Storage Manager tool to run a SMART Quick Test or a full Extended Test. The Health Info will show SMART status and useful disk information including Temperature (90F on mine). I configured Notifications to send me a monthly report; I didn’t want to give it access to my primary Google account so I used a non-critical secondary account for email services.
Synology tells me I have 3.6TB of storage to play with. That’s enough for my backups, but it doesn’t leave much for other uses. I considered using a Disk Group to create a 7.2 TB “drive” and divide that into two volumes, but then I did the arithmetic on failure assuming a 1/10 chance of drive death in the first year of use (which, for me, would be typical):
  • Use one drive for backup without drive group: 1/10 chance of data loss.
  • SHR data loss probability: 1/100 (both drives must fail, really it’s much less than that because they have to both fail before I can replace one)
  • Single Drive Group data loss probability: 1/5 (1 - 0.9*0.9) — Assuming data is striped so that if either drive dies the entire data group is lost.

I decided I like having a much more reliable backup — at least for now. I don’t like the risks of creating a Single Drive Group, but I could see one day using one drive for backup and another for other work.

You can only have one Time Machine folder on the Synology NAS that will hold one or more Time Machine disk images (one disk image per Time Machine), but you do have a choice about how many users to create. If you create one user with privileges for this folder they all share the same disk quota and the logs are hard to interpret. If you create one user for each Mac then each machine can have its own quota and the logs are more useful. I created one user per machine named after each Mac’s network name (they all share the same password). Each of these users has its own disk quota, I’ll have to see how Time Machine behaves with that. I gave each user “Network Backup Destination” and “File Station” application permissions, I’m not sure both are needed.

Synology supports AES encryption of the backup disk, but a 2012 article claims a major performance impact. Time Machine also supports encrypted backups (new since 2012) but for initial setup I’ve left that off. Since my primary server is also unencrypted this isn’t worse than my current practice. I use encrypted images for sensitive data and we do encrypt our laptops and our rotating offsite server backups. The primary risk of an unencrypted onsite drive is, of course, theft. When I have more experience I’ll experiment with Time Machine’s native encryption, but I wonder if that service has something to do with the impossibly slow Time Capsule restores I’ve seen.

As I finish this post my first Time Machine backup is starting — over Wifi, so this will take a while...

[1] Synology is a very Chinese product — including off-key English syntax. I wouldn’t install it in a US government facility.

Update: I’m realizing 3.5TB probably isn’t enough storage, and I’ve been told the Synology NAS keels over when asked to remove a TB sparsebundle. So after my initial testing I’m probably going to start over with two separate 4TB drives and create a separate volume for each machine I’m backing up. Then I can wipe the volume rather than delete the sparesebundle. Seems like the right balance between reliability and storage efficiency for my uses.

Update 3/11/2016

I ended up staying with the RAID redundant configuration; 4TB has been enough so far. I also found it’s not that bad to delete a large sparseimage — as  long as you do it from the Synology NAS using File Station (NOT from MacOS!). It takes about an hour to delete a multi-TB sparseimage.


R Lamirand said...

thanks. I did the exact same thing. screws wouldn't fit, removed all 8 drive screws to check I hadn't put the wrong ones in the wrong places. looked closely. pushed the little things really hard to work. getting frustrated... googled, found this, looked in box... yes another little tiny bag with two little tiny screws. lol, had to laugh at self, thanks again.

JGF said...

Glad it helped! Bet lots get confused. I did a facepalm.