SSD Caching with read/write
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SSD Caching with read/write
I have an extra bay in my TS-453mini that I put an Intel 545s SSD in there to try SSD caching.
Well... I'm bummed. I want a read/write cache but it warned me about data loss if I used a single SSD as a write cache.
Well, I thought, no big deal as long as it flushes the write cache when the system goes idle... plus Intel SSDs should be reliable enough and the SMART data should help warn me when the SSD is going to fail.
BUT.... there is no indication of how and when it flushes the data from the write cache to the RAID array... and I see no config options to control how this is done.
I would definitely use SSD caching if the NAS would frequently flush any write data to the RAID array (like when it went mostly idle). I don't want the data sitting on the SSD for hours or days or weeks without being flushed.
So...
1. When does it flush the write cache data?
2. Do I have any control over flushing the write cache?
3. Will it leave write-cached data on the SSD for hours and/or days and/or weeks without flushing?
UPDATE: Also see:
viewtopic.php?f=24&t=148431
Well... I'm bummed. I want a read/write cache but it warned me about data loss if I used a single SSD as a write cache.
Well, I thought, no big deal as long as it flushes the write cache when the system goes idle... plus Intel SSDs should be reliable enough and the SMART data should help warn me when the SSD is going to fail.
BUT.... there is no indication of how and when it flushes the data from the write cache to the RAID array... and I see no config options to control how this is done.
I would definitely use SSD caching if the NAS would frequently flush any write data to the RAID array (like when it went mostly idle). I don't want the data sitting on the SSD for hours or days or weeks without being flushed.
So...
1. When does it flush the write cache data?
2. Do I have any control over flushing the write cache?
3. Will it leave write-cached data on the SSD for hours and/or days and/or weeks without flushing?
UPDATE: Also see:
viewtopic.php?f=24&t=148431
Last edited by CommonSenseAl on Thu May 09, 2019 10:26 pm, edited 1 time in total.
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Re: SSD Caching with read/write
Irrelevant, whether it leaves it in cache for 2 mins to 2 days, you can still get data corruption if it fails.
Hence need for two.
Hence need for two.
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Re: SSD Caching with read/write
You can still get data corruption with two should they both fail.storageman wrote: ↑Thu May 09, 2019 7:17 pm Irrelevant, whether it leaves it in cache for 2 mins to 2 days, you can still get data corruption if it fails.
Hence need for two.
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Re: SSD Caching with read/write
Well hopefully they don't fail together and you swopout the first one that fails before the second one does!CommonSenseAl wrote: ↑Thu May 09, 2019 10:15 pmYou can still get data corruption with two should they both fail.storageman wrote: ↑Thu May 09, 2019 7:17 pm Irrelevant, whether it leaves it in cache for 2 mins to 2 days, you can still get data corruption if it fails.
Hence need for two.
It's all your decision.
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Re: SSD Caching with read/write
Yes, it's my decision.storageman wrote: ↑Thu May 09, 2019 10:18 pm Well hopefully they don't fail together and you swopout the first one that fails before the second one does!
It's all your decision.
And I want to use one SSD and have it flush frequently enough so that data does not stay only in the cache for hours or days or weeks... that is an acceptable risk to me. So back to my original question.
UPDATE: Also see:
viewtopic.php?f=24&t=148431
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Re: SSD Caching with read/write
You can't - system decides.
And I can't see Qnap changing that.
If you want to force a flush run "Check File System" - that would do it, but also take your volume offline temporarily so not something to do lightly.
And I can't see Qnap changing that.
If you want to force a flush run "Check File System" - that would do it, but also take your volume offline temporarily so not something to do lightly.
Last edited by storageman on Thu May 09, 2019 10:36 pm, edited 1 time in total.
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Re: SSD Caching with read/write
Thanks.storageman wrote: ↑Thu May 09, 2019 10:31 pm You can't - system decides.
And I can't see Qnap changing that
Do you have any idea how the system decides?
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Re: SSD Caching with read/write
Well... until I get more clarification on this I'm just going to use the SSD as a read-only cache... it's a bummer... it could be so much better with better write caching support when only one SSD is used.
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Re: SSD Caching with read/write
Until reading this thread, I was under the impression that the Write cache was indeed flushed "all the time", at least when the system was idle. That is not the case? Someone must know what the flushing parameters are???
Apple: MS M1 Max 10c/32c/16c/64GB/2TB - MP 3.2GHz 16c/192GB/2TB/2xRadeon Pro - nMP 3.5GHz 6C/64GB/1TB/D700 - Echo Express 1TB Accelsior/4x500GB NVMe Sonnet/Sonnet Solo10G PCIe - MBP 13" 4c i7/16GB/512GB - MBP 14" M1 Pro/16GB/512GB - MB 12" 4c i7/16GB/512GB - MMI 6c i5/8GB/500GB - 2 x TC 3TB - HomePods - iPhones, iPads and Apple Watches...
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Re: SSD Caching with read/write
Yeah someone does. It’s QNAP. Open a ticket and ask them and then report back here.
Use the forum search feature before posting.
Use RAID and external backups. RAID will protect you from disk failure, keep your system running, and data accessible while the disk is replaced, and the RAID rebuilt. Backups will allow you to recover data that is lost or corrupted, or from system failure. One does not replace the other.
NAS: TVS-882BR | F/W: 5.0.1.2346 | 40GB | 2 x 1TB M.2 SATA RAID 1 (System/VMs) | 3 x 1TB M.2 NMVe QM2-4P-384A RAID 5 (cache) | 5 x 14TB Exos HDD RAID 6 (Data) | 1 x Blu-ray
NAS: TVS-h674 | F/W: 5.0.1.2376 | 16GB | 3 x 18TB RAID 5
Apps: DNSMasq, PLEX, iDrive, QVPN, QLMS, MP3fs, HBS3, Entware, DLstation, VS, +
Use RAID and external backups. RAID will protect you from disk failure, keep your system running, and data accessible while the disk is replaced, and the RAID rebuilt. Backups will allow you to recover data that is lost or corrupted, or from system failure. One does not replace the other.
NAS: TVS-882BR | F/W: 5.0.1.2346 | 40GB | 2 x 1TB M.2 SATA RAID 1 (System/VMs) | 3 x 1TB M.2 NMVe QM2-4P-384A RAID 5 (cache) | 5 x 14TB Exos HDD RAID 6 (Data) | 1 x Blu-ray
NAS: TVS-h674 | F/W: 5.0.1.2376 | 16GB | 3 x 18TB RAID 5
Apps: DNSMasq, PLEX, iDrive, QVPN, QLMS, MP3fs, HBS3, Entware, DLstation, VS, +
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Re: SSD Caching with read/write
The "answer" I got from QNAP was:
I am still using my SSD as a read-only cache for now (until I get some answers anyway).
But I did upgrade the RAM on my TS-453mini from 2GB to 8GB... hoping that would help. Cost me a little over $50.
I am not even sure what that really means so if anyone can get a better answer then please post here!The SSD write cache flushes to the disk when the RAM is available.
No, there won't be any options or function to flush the cache to the disk. This is all done automatically the NAS.
I am still using my SSD as a read-only cache for now (until I get some answers anyway).
But I did upgrade the RAM on my TS-453mini from 2GB to 8GB... hoping that would help. Cost me a little over $50.
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Re: SSD Caching with read/write
Actually that answer does make sense. It basically means that you'll be writing to the SSD cache, and it will stay there until it can be offloaded to RAM, which in turn means it will be written to the data volume ASAP. So the process is; Computer -> SSD Cache -> RAM -> Data Vol.
Of course as you usually have a lot less RAM in your NAS than you possibly do SSD Caching, it can take a bit of time, but time here is seconds.
Of course as you usually have a lot less RAM in your NAS than you possibly do SSD Caching, it can take a bit of time, but time here is seconds.
Apple: MS M1 Max 10c/32c/16c/64GB/2TB - MP 3.2GHz 16c/192GB/2TB/2xRadeon Pro - nMP 3.5GHz 6C/64GB/1TB/D700 - Echo Express 1TB Accelsior/4x500GB NVMe Sonnet/Sonnet Solo10G PCIe - MBP 13" 4c i7/16GB/512GB - MBP 14" M1 Pro/16GB/512GB - MB 12" 4c i7/16GB/512GB - MMI 6c i5/8GB/500GB - 2 x TC 3TB - HomePods - iPhones, iPads and Apple Watches...
Primary NAS: QNAP TVS-872XT 7x10TB + 2x512GB NVMe SSD. BackUp: Cloud iDrive - Locally QNAP TR-004 4x12TB
Network: ISP Gtateway - TP-Link Deco - QNAP QSW-M408-4C
Primary NAS: QNAP TVS-872XT 7x10TB + 2x512GB NVMe SSD. BackUp: Cloud iDrive - Locally QNAP TR-004 4x12TB
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Re: SSD Caching with read/write
Interesting... well, when I decided to remove the SSD write cache, it took awhile to remove (turn off) while it seemingly wrote/flushed to disk.... so if it writes ASAP then why did it seem to work for awhile flushing the write cache when I turned it off? My NAS is just for home use and it's not very busy at all so if it was flushing constantly then I would think that turning off the SSD cache would be very quick because no flushing would be needed (since it would have been flushed already).bokr71 wrote: ↑Sat May 18, 2019 7:01 am Actually that answer does make sense. It basically means that you'll be writing to the SSD cache, and it will stay there until it can be offloaded to RAM, which in turn means it will be written to the data volume ASAP. So the process is; Computer -> SSD Cache -> RAM -> Data Vol.
Of course as you usually have a lot less RAM in your NAS than you possibly do SSD Caching, it can take a bit of time, but time here is seconds.
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Re: SSD Caching with read/write
I am not saying this is how it works. I am saying this is what the message from QNAP means. I also have seen it take a decent amount of time to turn caching off, which it says is due to the flushing of the write cache. But I think there is more than that going on...
Apple: MS M1 Max 10c/32c/16c/64GB/2TB - MP 3.2GHz 16c/192GB/2TB/2xRadeon Pro - nMP 3.5GHz 6C/64GB/1TB/D700 - Echo Express 1TB Accelsior/4x500GB NVMe Sonnet/Sonnet Solo10G PCIe - MBP 13" 4c i7/16GB/512GB - MBP 14" M1 Pro/16GB/512GB - MB 12" 4c i7/16GB/512GB - MMI 6c i5/8GB/500GB - 2 x TC 3TB - HomePods - iPhones, iPads and Apple Watches...
Primary NAS: QNAP TVS-872XT 7x10TB + 2x512GB NVMe SSD. BackUp: Cloud iDrive - Locally QNAP TR-004 4x12TB
Network: ISP Gtateway - TP-Link Deco - QNAP QSW-M408-4C
Primary NAS: QNAP TVS-872XT 7x10TB + 2x512GB NVMe SSD. BackUp: Cloud iDrive - Locally QNAP TR-004 4x12TB
Network: ISP Gtateway - TP-Link Deco - QNAP QSW-M408-4C