JimW

To SHR or not SHR, that is the question

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A little background...

 

I've been thinking about setting up a NAS for quite a while. Recently my family decided to digitize the entire stockpile of VHS and camcorder Hi8 home videos. After digitizing the first box, we calculate that it's going to take many terabytes to get it all done. Cloud storage is looking to be hundreds of dollars a year.  So I decided to pull the trigger and build a NAS to store them all along with all my other media. I have Roku's all through the house and purchased PLEX. Roku's have a great PLEX application. 

 

My co-worker suggested building my own NAS to save money and have a NAS capable of supporting PLEX transcoding and various other computing intensive activities desirable on a NAS. I'm using a Windows box with an I-3 processor and 12 GB RAM that was laying around. It had a couple of 500 GB drives and I added 2 more 4 TB drives with the expectation of upgrading the 500's over time. In another thread on this forum, I was told that all I needed was a supported SATA 3.0 expansion card with the port density I wanted and let DSM's software RAID controller do the work. I went with that advice and installed a four port SATA 3.0 card to give me 6 ports total including the 2 motherboard SATA 3.0 ports. Currently the 4 drives are attached to the card. I had small spare SSD drive that I connected to the motherboard that I intend to use as a cache. 

 

After the hardware build, I followed these instructions:      https://github.com/XPEnology/JunLoader/wiki/Installing-DSM-6.0-Bare-Metal    and successfully installed DSM from the .pat file linked to in this tutorial. Using the two 500 GB drives was based on my co-worker's experience of using SHR to have a redundant RAID setup with different sized drives and the ability to swap out a bad drive with a larger drive and/or upgrade to larger drives in the future. However after the install, when attempting to build the RAID group, there is no SHR option. Some quick research revealed that not all versions of DSM support SHR. Here's a page that lists those versions:

 

https://www.synology.com/en-us/knowledgebase/DSM/tutorial/Storage/Which_models_have_limited_support_for_Synology_Hybrid_RAID_SHR

 

Looking in the specs of my DSM install shows that it thinks it's a DSM3615xs device. Sure enough, this is listed on the above page as not supporting SHR. So my questions are, should I pursue trying to install a version of DSM that does support SHR with the xpenology boot loader? I really like the idea of being able to use what ever size drives I want. If I set up a traditional RAID, I'll need to purchase two more 4 TB drives now and then I'd have to start all over if I want to increase drive size instead of adding more 4 TB drives. If SHR is desirable, what version of DSM should I use and where do I get it?

 

Thanks 

 

 

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You're right that the DS3615xs no longer supports SHR out of the box, however it can be enabled but you have to SSH into the server & edit  /etc.defaults/synoinfo.conf, 
this file is readonly so enter following command:

sudo -i vi /etc.defaults/synoinfo.conf

comment out/delete
supportraidgroup="yes"

then add
support_syno_hybrid_raid="yes"

Once done reboot the server & SHR should be available as on option.

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if you are a 'newbie' to NAS/RAID etc, enable SHR and stick with that. Its software raid, but flexible adding disks of different sizes, data recovery, volume management etc.

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Dfds,

 

That is totally awesome!!

 

I'll give that a shot tonight and see how it works. Thanks a million.

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Posted (edited)

All good advice.  However, if you manually troubleshoot your volumes, a standard RAID1/RAID5 array is easier to work with than SHR (which is multiple RAID arrays joined via LVM).  So if you don't need that extra 500GB of storage, I'd leave those two off and just add to your array when you get additional, larger drives.

 

Also, consider skipping the cache.  It is less effective than you might think.  And much of the value is duplicated with the large amount of RAM you have which will write cache.  There are many, many instances of corrupted volumes due to SSD cache.  At a minimum, do some testing with and without cache for a workload you are likely to do.  I think you'll find that it isn't meaningful enough to warrant its use.

Edited by flyride

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Thanks flyride, that's good information.

 

Correct me if I'm wrong, but for RAID 5 the following limitations apply:

  • I need at least three drives of the same size (unless I want to under utilize the larger drives)
  • The only expansion I can do is add more drives of the same size or they will be under utilized
  • To use larger drives in the future, I'd have to replace smaller ones one at a time and rebuild
  • During the replacement cycle, the larger drives will be under utilized until all the smaller drives are replaced

Where does DSM install itself initially? Would it be possible to force the OS to install on the SSD drive and dedicate the SSD to that and the other apps I want to host like PLEX?

 

Thanks for all the great feedback everyone. 

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1 hour ago, JimW said:

Thanks flyride, that's good information.

 

Correct me if I'm wrong, but for RAID 5 the following limitations apply:

  • I need at least three drives of the same size (unless I want to under utilize the larger drives)
  • The only expansion I can do is add more drives of the same size or they will be under utilized
  • To use larger drives in the future, I'd have to replace smaller ones one at a time and rebuild
  • During the replacement cycle, the larger drives will be under utilized until all the smaller drives are replaced

Where does DSM install itself initially? Would it be possible to force the OS to install on the SSD drive and dedicate the SSD to that and the other apps I want to host like PLEX?

 

Thanks for all the great feedback everyone. 

DSM is installed to all HDD's, you can't choose where to install it.

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Posted (edited)

Yes, you need 3 drives for RAID5.  You can set up RAID1 and then convert to RAID5 when you have more than two drives, if needed.

Your other statements are accurate for RAID5.  SHR will allow you to mix drive sizes, but one of the largest drives will be totally reserved for parity.

 

As mentioned, DSM is normally installed to all drives.  You can isolate Plex to the SSD if you install it at a separate, Basic volume (obviously no redundancy). 

I do something like this with my system - 2x SSD's in RAID1 for Docker/Plex, 8xHDD in RAID10 for media files and other storage.

 

You actually can remove the DSM replicas and from specific devices - i.e. HDD's leaving DSM on SSD's, but it's a little obscure (and unsupported) how to do that, and there is no way to reclaim the space that DSM would have used.  It's a bit of an extreme tuning strategy and I would not consider it without having at least 2 devices for DSM. If you want to learn more read this: How to manage DSM to specific drives

 

Quote

Correct me if I'm wrong, but for RAID 5 the following limitations apply:

  • I need at least three drives of the same size (unless I want to under utilize the larger drives)
  • The only expansion I can do is add more drives of the same size or they will be under utilized
  • To use larger drives in the future, I'd have to replace smaller ones one at a time and rebuild
  • During the replacement cycle, the larger drives will be under utilized until all the smaller drives are replaced

Where does DSM install itself initially? Would it be possible to force the OS to install on the SSD drive and dedicate the SSD to that and the other apps I want to host like PLEX?

 

Edited by flyride
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@flyride: Thanks for the link to your article from march! I missed it and the information in it is very useful. :-)

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9 часов назад, benok сказал:

SHR has several drawbacks on upgrade, if you want to use SHR,

I recommend you to read this article carefully.

 

Don't Roll Into Trouble When Expanding NAS Storage - SmallNetBuilder https://www.smallnetbuilder.com/nas/nas-features/32649-don-t-roll-into-trouble-when-expanding-nas-storage

 

I stopped using SHR after I read this.

 

Its not only shr problem. But the information by the link told about expansion of array after disk change.

So its not only shr, but a ussual raid problem. 

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