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Nick-SAC
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Synology NAS - iSCSI - ReFS

Post by Nick-SAC » Jul 23, 2019 2:02 am

Synology DS918+ running DSM 6.2.2-24922 Update 2

Either I’m missing something or the newer versions (apparently 6.2 up) of Disk Station Manager (DSM) have eliminated the ability to configure an iSCSI attached ReFS Formatted Volume.

There used to be an item in the DSM Storage Manager to a Create a Block Level iSCSI LUN (which would then be located directly on the iSCSI Target Storage Pool ) but that’s no longer there and in the new iSCSI Manager it will only let me create a LUN on a previously created (BTRFS formatted) Volume.

Curiously, if I do that; when I establish the iSCSI Connection to the Windows Server (2019) Windows appears to let me format it as ReFS (I’ve only tried a Quick Format) but the Volume still shows as BTRFS from within DSM – and I can’t even venture a guess as to what that means?! ... Or how it will or won’t work?!

FWIW, I’ve got 2 other Synology NAS units (a DS918+ and a DS412+) which were configured under DSM 5.2 or 6.1 with the iSCSI LUN Located directly on the iSCSI Target Storage Pool (no Volume exists on the NAS) and they’re still working fine even though they’re also now running DSM 6.2.2-24922

I’ve just opened a Support Ticket with Synology on this and will report what I find out... but if anybody has a suggestion, I’d love to hear it!

Nick-SAC
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Re: Synology NAS - iSCSI - ReFS

Post by Nick-SAC » Jul 24, 2019 3:13 pm

I haven’t received a response from Synology yet but in the meantime...

I’m currently experimenting by performing a Full (not Quick) ReFS Format from the Win2019 Server on the iSCSI attached Target/LUN which is (as seen from within DSM on the NAS) a BTRFS Formatted Volume.

Does anybody know if this ReFS/BTRFS scenario will work and/or if it is an advisable or even supported configuration?

Nick-SAC
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Re: Synology NAS - iSCSI - ReFS

Post by Nick-SAC » Jul 26, 2019 4:31 pm

Here is the response from Synology...

================================->snip<-================================

The luns which were directly on the storage pool were known as block level luns. After DSM 6.2, our developers removed the option to create block level luns. Once which previously existed will continue to work.

The block level luns did not perform as well as file level luns, so you should actually be better off with a file level lun. We would recommend making sure you are on the latest version of DSM, creating a btrfs volume, then create a thick provisioned file level lun with the default features chosen. We recommend not creating luns which consume more than about 90-95% of the volume to prevent the possibility of the volume filling to capacity, since the system does need some space on the volume for system files and general operation, and also it is possible for a lun to consume slightly more than the allocated amount due to any fragmentation.

You mentioned "it will need to be formatted ReFS but on the NAS the Volume that the LUN would be on is BTRFS and that (even if it would appear to work) seems like it'd be asking for trouble..."

This shouldn't be asking for any trouble. The NAS just obeys the commands from the iscsi initiator, it does not actually read the data or even know what filesystem is on it, or if there is a filesystem on it at all. So the choice of filesystem will make no difference on a block or file level lun.

Sincerely,
Carl W
Synology Tech Support

================================->snip<-================================

Frankly I’m not entirely comfortable with this BTRFS/ReFS issue but it seems to be working properly so far in as much as the Full ReFS Format from the Win2019 Server proceeded without error (although it took 18 hours for a 10TB Volume over a 1Gbps LAN).

After I get some VM’s in place on this Server and do some Backups & test Restores I’ll report the results but I’d still welcome any input from someone more well versed than I in the FS issues.

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