Synology Time Machine Backup – The Quota Option

Back when I first wrote about using the Synology NAS for Time Machine backups I had decided to go with a volume dedicated to Time machine. A recentcomment to that post, asking about quotas, got me thinking about alternative configurations. Especially since this coincided with me reconfiguring my DS 1511+ NAS. A dedicated time Machine volume on that was more limiting than I want. So I did some more testing and came up with a quota method on existing volumes which I’m now using.

DS1511+ FrontBack when I first wrote about using the Synology NAS for Time Machine backups I had decided to go with a volume dedicated to Time machine. Since then I’ve cut back it’s us, using it only for my Mac Mini. Greg recently posted a comment to that post, asking about quotas, which got me thinking about alternative configurations. Especially since this coincided with me reconfiguring my DS 1511+ NAS. A dedicated time Machine volume on that was more limiting than I want. So I did some more testing and came up with a quota method on existing volumes taht aren’t dedicated to Time Machine.

Essentially, this is the problem to be solved:

  • Time Machine is designed to keep backups until a drive is full and then delete the oldest backups to free up space.
  • A share is assigned for Time Machine in the Synology DSM software. Only one share can be used across all computers.
  • Shares will use as much pace as available on the volume.
  • Quotas are user based and apply to an volume, not a share. If there are multiple shares on a volume, the quota is applied across them all for the user.

So the choices are to use a dedicated volume for backups and allow it to be filled, or use an ID dedicated to backups and set the quota on it. This article covers the latter option.

Requirements & Notes

I’ll need an ID dedicated to Time Machine backups. A ID could be shared across Macs but I decided to go with individual IDs per Mac. This gives me slightly more flexibility in the way I manage quotas.

I found that Time Machine does not handle quota changes. It appears that when Time Machine first attaches to a drive (or share) it registers how big the drive is. Even though Time Machine saw the extra space after a quota increase (in it’s space available display) when it got down to the actual backup it based the backup on the old quota. For example, I had to delete the Time machine backup for the Mac and have it start over after I increased the 1 GB quota I used for testing. . I suppose I could have copied the old files for safe keeping, but this was just testing. This isn’t much different than a physical disk, but it would have been nice to have the flexibility.

This works on my DS 212J and DS1511+ NASs. Both are running DSM 4.0-2219, which is the latest version at this time. My Macs are running OS X 10.7.3 Lion, also the most recent version.


The setup process includes creating the share, enabling TIme Machine in DSM, creating the IDs in DSM and finally, setting up Time Machine on the Macs. Click on any of the images in this section to see them full size.

Create the Share

First off I’ll set up the Time Machine shared folder using the DSM control panel.

Screenshot of the Synology Control Panel

Create the shared folder.

Enable Share

Don’t setup any privileges yet so just click OK on the privileges screen without enabling any access. I don’t want any of the regular IDs to have any access to this share.

Create the User(s)

This is also done through the Synology DSM Control Panel.


Create a new user


Fill in the user information


Click OK on the groups screen and allow the user to be a member of the Users group. (For this purpose I don’t think it needs to be a member of any group, but I’ve yet to test it and I’m not all that concerned with security for this ID.)


Give the user access to the Time Machine share.


Set the quota for the volume that the Time Machine folder is on. This is how much space the ID can use for Time Machine.


There’s no need for additional privileges so I disable access to the applications.


After confirming the setup I’m done. I repeat the steps for a second ID, setting a 500GB quota for the ID MBUser.

Enable Time Machine on the Synology NAS

Time Machine is enabled through the DSM Control Panel


Enable the Mac File Service and select the Time Machine shared folder.


Click Apply and acknowledge the warning that network services will restart.

Setting Up Time Machine on the Mac

This is a normal Time Machine configuration, but I’ll run through it.

Open Time Machine Preferences.


Click the Select Disk button. The Synology NAS should appear in the available drives. I the screenshot below both my test and production Synology NAS’s are shown. Normally you’d see just one Synology NAS listed.


You’ll be prompted to provide an ID/password. Enter in the ID created above.


Time Machine will begin a countdown to start a backup. You can make any exclusions at this time. (For example, I exclude my virtual machines directory on my MacBook Air so I don’t back them up over wireless.) You’ll also see the amount of free space. In this example, the volume the share is on is 10TB in size so it is seeing the 250 GB quota.



Further Testing & Wrapping Up

I’ve only used this configuration a short time so it’s long term viability is still undetermined.  I have setup my test server with smaller quotas and on a smaller volume so I can see what happens when the quota is reached. I also want to see what will happen when other files consume so much of the volume that there’s less than the quota available to Time Machine, I’ll come back and update this post when I have that information.

So far I haven’t had any problems connecting to shares using my regular ID from the Macs that have Synology Time Machine configured.

I’m still skeptical of using Wireless to backup Time Machine, which is unrelated to Synology. I have a pretty reliable wireless connection but there’s still the relatively slow speed. If I’m doing other work that makes heavy use of wireless the Time Machine backup could impact that. I’m going to leave it setup, at least until it causes a problem. I’ll come back and update this post if it does and I’ll include a status in my next Trail Log.

Anyone else have any experience using Time Machine servers, Time Capsule, Synology or others?

5 thoughts on “Synology Time Machine Backup – The Quota Option”

  1. Thanks for the article. You’ve mentioned concerns about using Time Machine to the NAS over wifi. Is there any backup method that you would endorse over wifi? I’m a little puzzled about this issue. Unless my wifi is really spotty (losing it’s connection) I don’t see why wifi, however slow, should equate to this kind of task outright failing. The underlying protocol, TCP, has reliability/retry built in. and in the event that TCP does throw up an error, the backup software should retry. The job should get done, it’s basically just a lot of large and small files. Must be something flakey about Time Machine, poor error handling?

    I’ve used carbon copy cloner to a NAS. Only downside is it requires that the target be a disk image. So before the backup begins, it must mount the .dmg on the NAS, then start reading/writing it. Since that’s going to be a very large disk image, it may take a while. But it does work.

    1. @Brendan – My wireless concern is the quality of the wifi and losing connections long enough to drop. TM is fairly complicated since it’s a lot of pointers to files and much like a database. Similar concerns with similar backup apps. The other reason I wasn’t using it is my virtual machine images would take too long to backup. I didn’t want to leave my laptop on overnight for backups and I didn’t want a constant file copy going on when I was working or when I was trying to stream video over wireless. Now I excluded the VMs and it’s been fine.


  2. Hi Ray, thanks for this article. I’m currently evaluating the merits of the quota vs dedicated volume approaches to limiting the size of Time Machine backups on my Synology NAS.

    Was wondering if you ever figured out what happens when the volume gets filled up by other users leaving less available room than the quota initially setup for the Time Machine user.

    Don’t mean to rush you, just have to ask as I’m uneasy moving ahead with this unknown looming over the fate of my data.

    Thanks for any info or advice you can provide,

    1. @Richard – I’m using the quota method for two PC’s, each using a different ID so with it’s own quota. I did force low space and Time Machine was fine. It treated the low space like a full disk and simply deleted the oldest backups. When space freed up TM would reclaim it if needed.

      Two minor issues. I created new files on my Mac just under the free space available in the quota and started a TM backup. While that backup was running I copied files to the NAS disk to fill up the space so there wasn’t enough for the new files. The TM backup errored out. and since there wasn’t enough space for the new files TM told me to get a larger disk. When I deleted files on the Mac and deleted files from the NAS the next TM backup was fine.

      Similarly, TM wants to be able to save data going back some amount of time (not sure what that timeframe is). so when I filled the disk the first day TM simply told me to get a bigger disk as it was unhappy with only a day of data.

      Overall the TM backup to Synology seems resilient. I do have occasional issues with my MacBook Air but I think that’s due to wireless. I’ve had two cases where TM decided it needed to do an entirely new TM backup. my wired Mac Mini has been solid.

      Thanks for stopping by.

      1. Fantastic! Thanks for sharing these results, much appreciated. Sounds robust enough for me and I will move ahead with the quota approach.

        Take care,

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