TS-879U-RP SSD Caching

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sweepscape
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TS-879U-RP SSD Caching

Post by sweepscape »

Hi,
Just have a couple questions around the TS-879U-RP model and it's SSD cache function.
http://www.qnap.com/en/index.php?lang=e ... n=3425&g=1

1. First is around vmware, if you have a vm datastore with several terabytes worth of virtual machines but say 1Tb of ssd cache applied, is the ssd caching on these devices intelligent enough to cache active data inside the virtual machines? not simple just try to cache the vmware datastore files like the vmdk files etc.

2. Just looking at these models in Australia, stores that claim to stock this specific model seem to suggest slightly different features like 2x 1Gb nics for example (as apposed to 4x 1Gb listed on the QNAP website), that's not a big deal since I can install a nic if need be but none of the sites specifically state that the TS-879U-RP supports SSD caching like the QNAP product page does. Can anyone confirm whether this version being sold in AUS supports SSD cache? I got the impression from the QTS 4 promotional video on the QNAP website that the ssd caching function was introduced as a software feature for specific models like the TS-879U-RP, so my thinking was that perhaps these stores in AUS are shipping their QNAP's with QTS 3.x. If it's a matter of a simple OS update once the device is purchased, then that's fine, but I don't want to purchase one of these units only to find out it's not supported.

example listing:
http://www.cplonline.com.au/qnap-ts-879u-rp.html
tombulum
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Re: TS-879U-RP SSD Caching

Post by tombulum »

Can't help with your first question, but can answer the second.

The SSD caching function was added to QTS 4 for certain high-end devices (which includes the TS-879U-RP).
I bought mine about 4 months ago in Melbourne from CPL, and when I looked at the specs it only had 2 network ports and 2 memory slots.
The one I received had 4 network ports and 4 memory slots.

Have a look at my posts:
http://forum.qnap.com/viewtopic.php?f=12&t=79843
http://forum.qnap.com/viewtopic.php?f=1 ... 2&start=30

I don't know if the same, later version is the only one that's in the supply chain in Australia, but I would say it's highly likely that you would get the newer model.
Primary: QNAP TS-h1283XU-RP w/ 10 x Seagate EXOS 16TB in RAID-TP
FW QuTS Hero H5.0.0.1949 / 32 GB ECC RAM / Built-in 10 Gig network
Backup #1: Synology RS3617XS+ w/ 10 x Hitachi Ultrastar 10TB in RAID 6
FW DSM 7.0.1-42218 Update 3 1 / 8 GB ECC RAM / Built-in 10 Gig network
Backup #2: QNAP TVS-863 w/ 8 x Hitachi Deskstar 6TB in RAID 6
FW 5.0.0 / 8 GB RAM / LAN-10G2T-X550
Ternary: 2 x QNAP TS-879U-RP w/ 8 x WDC Red 4TB in RAID 6
FW 4.3.6 / 32 GB ECC RAM /
Ternary: QNAP TS-470 Pro w/ 4 x WDC Red 4TB in RAID 6
FW 4.3.6 / 16 GB ECC RAM /
rinthos
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Re: TS-879U-RP SSD Caching

Post by rinthos »

RE: Question #1, nope SSD caching is not that smart, it can't cache a "partial" VMDK...at least based on my testing.. sorry. :(
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sweepscape
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Re: TS-879U-RP SSD Caching

Post by sweepscape »

Thanks for the responses, doh re the ssd caching on the vm's, certainly seems like it'd be a great feature to have.
QNAPJauss
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Re: TS-879U-RP SSD Caching

Post by QNAPJauss »

Hi sweepscape,

Here some clarifications :
is the ssd caching on these devices intelligent enough to cache active data inside the virtual machines?
Yes, the SSD cache is that smart !!
To be more precise, SSD cache function do not cache any files... the cache is block-based. Let me explain :
- you have your datastore, where SSD cache is enabled on the QNAP.
- You create a VMwith its VMDK in the datastore
- Inside the VM, you will have some files that need to be accessed very often.
--> When you access those files, you will read some block of data on the NAS. If you read those block of data, often, they will be stored in the SSD cache to make it faster to access.
--> The will be transfered only for Random IO : if you just copy large file, the benefits will be limited, but if you boot the VM, have a database, the benefits will be important.
The SSD cache will not be used for sequential reads because we optimized the cache for random IO, as the latency (access vtime) on SSD is faster then one HDD.

When some files are accessed in the VM, their block of data can be cache in the SSD cache if necessary (random IO).
TS-879U-RP supports SSD caching like the QNAP product page does.
Yes, The TS-879U-RP support SSD Cache with the new firmware QTS 4.0 or above.
If the NAS already have 3.x firmware, it can be updated to 4.0.
The TS-879U-RP supports up to 2 SSD for cache.


BR,
Jauss
sweepscape
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Re: TS-879U-RP SSD Caching

Post by sweepscape »

Brilliant, thanks for clarifying, in this case, the customer isn't running any over large files, biggest files would probably be autocad drawings. It's just a few VM's like AD, Exchange and Terminal Server and a database with upwards of 500,000 tiny files. Currently they run this off an old HP StorageWorks X1600 server in Raid5, incredibly slow.
rinthos
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Re: TS-879U-RP SSD Caching

Post by rinthos »

@QNAPJauss

Is it possible that the QNAP NAS caching is deciding to not cache due to the read pattern noticed when booting a VM from a VMDK container?
500GB VMDK running windows 2008. Continuously rebooting over and over does not appear to benefit from SSD cache in my testing...(w/ a 128GB sandisk drive)..and i see a lot of disk activity w/ each reboot..

With mp3 files being scaned with anti-virus files, I notice quite the opposite result. First scan is a little slow, but all subsequent scans are much faster and i see little disk activity...

Is there any fine tuning I can try for the VMDK workload?
QNAPJauss
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Re: TS-879U-RP SSD Caching

Post by QNAPJauss »

Hi rinthos,
Is it possible that the QNAP NAS caching is deciding to not cache due to the read pattern noticed when booting a VM from a VMDK container?
Yes, if the IO are sequential or for large block, SSD cache may not be used because.
However, even if some data is not cached because of some sequential IO, when a VM boot the random IO are much higher, and the cache may be used to optimize the access to those random IO.
500GB VMDK running windows 2008. Continuously rebooting over and over does not appear to benefit from SSD cache in my testing...(w/ a 128GB sandisk drive)..and i see a lot of disk activity w/ each reboot..
possible solution / explanations :
If you have a 500GB vmdk and only reboot the VM, not all the 500 GB will be used, so the NAS will not cache the 500 GB, but will cache only the few GB needed to boot.
Also, the NAS used filesystem cache, that may influence on the SSD cache hit. If only 1 VM is constantly rebooting, most of data will be in the filesystem cache, so the SSD cache may not be used.
For you tests, you can try to contently reboot 3~4 VMs, you will see the impact of SSD cache:
(multiple VM boot will produce more random IO than only 1 VM)
- hit rate increasing from on the UI.
- SSD cache space usage growing
Also, when a VM reboot, there is a lot of write that also cause disk access.
With mp3 files being scanned with anti-virus files, I notice quite the opposite result. First scan is a little slow, but all subsequent scans are much faster and i see little disk activity...
First slow scan: the SSD cache is empty. SSD cache need to learn where is the "Hot data", so when you enable SSD cache, the benefits are not immediate.
Other scan: 2 possibilities :
- SSD cache is used because all files are fragmented : lower disk activity
- depending what antivirus you use, the filesystem cache or the Windows OS cache may also be used depending on how much data you scan.
- Scan files is only read operation where VM boot is read/write operation.
Is there any fine tuning I can try for the VMDK workload?
Currently, we do not provide the option to change it.
but :
- if you copy/paste 1 VMDK, the SSD cache may not be used a lot because : sequential IO and large block read pattern
- when VM reboot : the IO would be random and smaller. the SSD cache will be used.

Also, you can select which volume or LUN you want to enable SSD cache
yani1shu
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Re: TS-879U-RP SSD Caching

Post by yani1shu »

Is it possible to see what files are being cached?
bertdb
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Re: TS-879U-RP SSD Caching

Post by bertdb »

yani1shu wrote:Is it possible to see what files are being cached?
No, because files aren't being cached. Blocks are being cached.
gimp_dad
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Re: TS-879U-RP SSD Caching

Post by gimp_dad »

Jauss,

Thanks for all of your helpful answers. I have another SSD cache question:

Does the SSD cache perform any write buffering or write allocation?

I know the documentation says it is a write through cache but I want to know if write performance is influenced at all by the cache or not. I have a database and will be doing random writes along with lots of random reads. With the SSD cache I was hoping to using RAID5 config to optimize space and cost per TB. However, if this becomes a huge write performance issue then I will have to set up the spinning media in RAID10 instead. I don't want to experiment with both solutions to find out the answer as I am just about to install the TS-879U-RP in my small business. I have been using a TS-439PRO II in RAID5 mode mainly as a backup file server and am aware of how slow RAID5 can be for write intensive applications.

Thanks for any help.
gimp_dad
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Re: TS-879U-RP SSD Caching

Post by gimp_dad »

Idelwizard, a write-through cache can be either write-allocate or not. That's why I'm asking the specific question about this product. In both cases a write goes all the way through to the main store. With write-allocation, a write to a cache line that is not in the cache causes an allocation (a fetch of that line from main store to the cache) such that subsequent accesses to that line will hit in the cache. Without write allocation, the cache miss via the write does not result in an allocation and thus does not fetch the line from main store. Saying it is write-through does not imply one or the other which is why there is such a thing as write-allocation or no write-allocation in the first place.

This is not to be confused with a write-back cache which also has write-allocation as an option but never writes back to the main store unless a line gets retired.

A write buffer is independent of whether there is write-allocate or not and simply aggregates a few writes in a row to allow a line sized block to be written to the main store at once. It generally takes care of making sure the writes stay in order and coherent such that a read to an address in the write buffer can't bypass the written value. These specifics will have a big impact on intensive database write performance for Raid5 vs Raid10. If there is a write buffer or if write-allocation effectively causes behavior like a write buffer then the write performance will be a lot less impacted by the fact that a Raid5 config requires a read modify write in order to carry out a write.
Peter.Parker
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Re: TS-879U-RP SSD Caching

Post by Peter.Parker »

Sorry for bumping an old thread. I just inherited one of theses boxes. Do the SSD go into the disc tray or is there a place inside.
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Re: TS-879U-RP SSD Caching

Post by OneCD »

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