New Plex NAS build. Using SSD Caching make any sense?

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jordan12

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I have a Raid 6 14TB X10 for 101TB available. I can slap in one or two SSD's as caching. Not 100% positive I fully understand the concept. But when I copy large files to the NAS, it seems write around the same speeds as my old one. About 120mb/s. I slapped two 512GB SSD's and then copied something, and about the same speed. I thought using two drives would allow read and write. At least that is what my NAS directions stated.

I made sure that were set up correctly on the NAS software. So no change in speeds. Do I simply not understand what caching really does?
 
Yep. 125 MB/s is the max throughput for gigabit ethernet, and in reality it's bit less once you account for overhead.

I'm not aware of any supplemental caching scheme that will really benefit a setup intended for large files that don't require high throughput (i.e., the bandwidth required for even 4k is well below that of gigabit ethernet) and are read sequentially, low network bandwidth relative to that of the storage itself, and only a few users. What's provided out-of-box from otherwise unused RAM should be more than sufficient.
 
I have a much smaller setup, with 4x10tb drives. I run 2x512gig in Raid1 for read/write cache. File operations are much quicker since the addition of the cache, and any transfers of small files are a lot faster.

I have 2.5gig networking to/from it
 
Plex build a database-library of your library, with thumbnail, tag like the director, year, genre for search and stuff like that you can set that folder to be on the ssd
 
As others have stated you're basically saturating your 1GbE. You'll want to look into 2.5GbE (~300MB/s transfer over network) or 10GbE (~1200MB/s transfer over network). This would involve putting a capable NIC in your server and workstation, as well as having a network switch that supports those speeds.

You can use this calculator: https://wintelguy.com/raidperf.pl to estimate performance on your RAID6 array. If you can directly copy files from the RAID6 array to itself and monitor it that could show you speeds. I think if you do it over the SMB share it would still be limited to the 1GbE network speed but I'm not 100% sure, I think this would have to happen directly to and from the RAID6 array (like RDP session or SSH access or something.)

In general I don't think running caching SSDs will help you on performance. On my home servers I've always ran OpenZFS without adding any sort of SSD (ZIL, SLOG or L2ARC) and I get good speeds read/writing to the array based on the network speeds and what I would expect out of the RAIDZ array. I would expect the same for a RAID environment.
 
I respectfully disagree with a lot of the people here.

Write caching will mean that random access (eg Plex indexing) won't directly hit the drives, it'll stay in cache, which means that you'll get a steady 1gbe generally speaking.
 
Keljian said:
I respectfully disagree with a lot of the people here.

Write caching will mean that random access (eg Plex indexing) won't directly hit the drives, it'll stay in cache, which means that you'll get a steady 1gbe generally speaking.
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OK, yeah, I suppose it's possible to have an all-in-one type setup on a NAS where the volumes/datasets for apps like Plex and its index/DB, and the media itself are housed on the same pool. A cache may help a bit there. A better design, I believe, would be to create a second pool using the SSDs to hold apps and any metadata they store.

If Plex or whatever app is on a separate system and just pulling media from the NAS, the NAS's caching scheme is irrelevant to the performance of the app's serving of metadata.
 
BlueLineSwinger said:
OK, yeah, I suppose it's possible to have an all-in-one type setup on a NAS where the volumes/datasets for apps like Plex and its index/DB, and the media itself are housed on the same pool. A cache may help a bit there. A better design, I believe, would be to create a second pool using the SSDs to hold apps and any metadata they store.

If Plex or whatever app is on a separate system and just pulling media from the NAS, the NAS's caching scheme is irrelevant to the performance of the app's serving of metadata.
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Yes and no - SSDs have very fast small random writes vs hard drives. It all depends. I agree a better design is to have the indexing and other stuff on a different device, but that means more power and more to manage.
 
What NAS are you using? I've been messing around with this exact same situation except for emby and truenas. I even went with 10gbe networking. I cant tell the difference between my 4x20gb drives with or without an ssd for reading or writing.

Granted, my full battery of tests isnt done, but right now an ssd seems like a waste.
 
applegrcoug said:
What NAS are you using? I've been messing around with this exact same situation except for emby and truenas. I even went with 10gbe networking. I cant tell the difference between my 4x20gb drives with or without an ssd for reading or writing.

Granted, my full battery of tests isnt done, but right now an ssd seems like a waste.
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I'm running a Synology 420+, with 4x10tb drives, 2x512gb SN700s, 18 gig of ram and a 2.5gig usb network adapter.

Plex and the unifi controller, as well as some of the logging I'm doing, are constantly accessing the drives. Since putting in the cache, the whole nas is quieter/uses less power, and I get higher iops.
 
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