M2D17 for Storage, not Cache?

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malooooone
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M2D17 for Storage, not Cache?

Unread post by malooooone » Tue May 16, 2017 7:00 pm

So in my specific use case I have a lot of purely sequential reads and writes, which is one of the situations where SSD cache is of arguable benefit. One thing I have noticed, though, is that having a 100% SSD volume configured (either single disk, RAID 1, or RAID 10) and using it as the target for package installs noticeably improves the responsiveness of those packages as well as the UI of the system as a whole. The main drawback has always been the loss of one or more drive slots to accomplish this.

Here is where the DS1817+ with an M2D17 comes in. I have several matching spare M.2 SSD's, and I would love to be able to use the M2D17 adapter to put two of them in a RAID 1 for use as this small operating volume, but all of the documentation I have read in regards to the adapter is strictly regarding use as an SSD cache device. As far as I know there should be nothing preventing the configuration of drives connected via the PCIe adapter from being used with any mode of storage, including cache, and it is possible that the limited capacity of M.2 drives relative to 2.5"/3.5" drives may be the only reason Synology is not touting this as an option. It is also possible that this is a true restriction either of the specific adapter card or of the DS software, and standard storage or RAID is not possible on that interface.

Does anyone have any insight on this, or is ordering in an M2D17 to try it out for myself the only real way to know? In the end I can always just use it for SSD cache, although that would preclude 10Gbit networking by occupying the slot...

malooooone
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Re: M2D17 for Storage, not Cache?

Unread post by malooooone » Thu Jun 08, 2017 7:28 pm

OK, I have bitten the bullet and ordered an m2d17, I will post back once I have the opportunity to install and test the available configuration options.

sincarne
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Re: M2D17 for Storage, not Cache?

Unread post by sincarne » Thu Jun 08, 2017 8:56 pm

malooooone wrote:OK, I have bitten the bullet and ordered an m2d17, I will post back once I have the opportunity to install and test the available configuration options.
gracias! would also like to see this on more model

malooooone
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Re: M2D17 for Storage, not Cache?

Unread post by malooooone » Fri Jun 09, 2017 2:41 pm

Small setback, I missed in the documentation where it stated that NVMe drives are not supported. Of all of my spare M.2 drives the only matched pairs I have are NVMe, so I will need to wait until I can pick up an M.2 SATA drive that matches one I already have.

Interestingly since the NVMe drives I installed are not supported there is no indication whatsoever that the M2D17 adapter is installed. I can't find anywhere on the system that indicates it detects the adapter at all, so I will need to wait to see where the system displays the adapter until I have compatible drives, if it ever does.

Pierre118
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Re: M2D17 for Storage, not Cache?

Unread post by Pierre118 » Mon Jun 12, 2017 8:01 pm

Is it neccesary to have 2 SSD in the M2D17 expansion board? Or does 1 work as well?

malooooone
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Re: M2D17 for Storage, not Cache?

Unread post by malooooone » Tue Jun 13, 2017 2:44 am

Well, I am sad to report that the M.2 SATA disks on the M2D17 card do indeed only show up as available for cache, and not for standard storage. Everywhere in the Storage Manager ignores them completely besides listings in the HDD/SSD tab, where they are given drive numbers of "Cache device 1-1" and "Cache device 1-2" with locations of "DS1817+, PCIe 1, M.2 slot 1" and "DS1817+, PCIe, M.2 slot 2" respectively.

I have to say I am disappointed, even though the device is marketed as being for cache only and this result was mostly what I expected. I really would love to have an SSD RAID 1 on the card for the additional space even if it was a bit limited by the form factor, and I don't see any reason why this couldn't be enabled, but I'm sure this is not in the queue for Synology's developers so I will just take my cache and use it for what it is worth. As another note adding cache has RAM overhead which I had been too lazy to calculate ahead of time, but while configuring a ~496GB cache the system indicated that it would use less than 200MB of additional RAM.

To answer the question above mine, with a single drive you can create a Read cache, but you need two drives to create a Read/Write cache. You also must assign each drive or pair of drives to a specific volume or iSCSI LUN, so if you have multiple volumes you could theoretically use two drives to create Read caches for two volumes instead of a Read/Write cache for a single volume.

Pierre118
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Re: M2D17 for Storage, not Cache?

Unread post by Pierre118 » Tue Jun 13, 2017 9:30 am

@Malooooone Thanks for the report and answer to my question. I also hoped that the SSD's were available for storage too, maybe on future DSM releases?

Redflyer
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Re: M2D17 for Storage, not Cache?

Unread post by Redflyer » Thu Jul 27, 2017 7:22 am

I too didn't read the small print so I have a couple for the Samsung 1TB EVO NVMe cards to play with on a DS1517.

I managed to build the nvme kernel module and it loads fine, I can also make a filesystem on the NVMe and mount it, all from the ssh command line I might add. What I really wanted to do was see if I could add it as cache for my RAID5 but the flashcache_create command failes to load the flashcache kernel module.. Needless
to say the disk manager doesn't pick it up.

flashcache_syno: Unknown symbol syno_flashcache_proc_lock (err 0)

A while back I checked a diskstation running with a SATA M.2 cache and it was using flashcache but I didn't check what other modules it depends on.

I can't think why Synology would not enable the use of NVMe, all the bits to make it work appear to be there, mayne because they haven't certified it?

guohan0917
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Re: M2D17 for Storage, not Cache?

Unread post by guohan0917 » Thu Nov 02, 2017 4:13 am

Hi Malooooone,

I just bought the M2D17, but too bad I missed out the M2 card.
If without the M2 card, do I able to enjoy the 40TB capacity or I only able to enjoy 20TB if I configure RAID5 ?

Appreciate you able to share the experience.

Thanks.

Regards
GuoHan

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