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Re: RN516 with SSD on OS 6.9

Xatosch
Apprentice

RN516 with SSD on OS 6.9

Hi...

 

At the moment my 516 is equipped with 5 hard disks, 3TB each. As I read in version 6.9, you can use an SSD as a cache. Good idea, I have a slot free and an SSD is available, too, but:

Does that work? Just put an SSD in the shaft?
Well, switching to FlexRaid shouldn't be the problem, but then? I mean, to have read that you need at least 2 SSDs?

How large must the SSD be?

So, what's it really cached? I use the Storage Spaces on a PC from Microsoft, there with 3 HDD and 2 SSD (multitier) and have a corresponding caching, divided into hot and cold data, is this similar?

Model: RN51600|ReadyNAS 516 6-Bay
Message 1 of 8
Xatosch
Apprentice

Re: RN516 with SSD on OS 6.9

*ping*

Message 2 of 8
mdgm-ntgr
NETGEAR Employee Retired

Re: RN516 with SSD on OS 6.9

Metadata is data about data, it’s this that can be tiered in 6.9.0. See ReadyNAS OS 6.9 Metadata Tiering.

 

Tiering does work better with multiple SSDs as you can use a redundant RAID level.

 

If your volume is RAID-0, then whether a single disk or a single SSD takes down your volume doesn’t make much difference.

 

If you look at btrfs.log you’ll see how much metadata you have. Metadata Tiering doesn’t require that much capacity.

 

The process to add a metadata tier is described in ReadyNAS OS 6.9: Adding a metadata tier to an existing volume

 

Tiering and caching are two different things though they may seem to be similar.

Message 3 of 8
Sandshark
Sensei

Re: RN516 with SSD on OS 6.9

The article on Metadata tiering is not very illuminating.  It does not say how metadata tiering helps, just that it does so for certain write operations.  It does not say what additional risks it adds in the case of loss of the SSD(s), just that more than one is "recommended" for unlisted reasons.  And it tells you "Before adding a metadata tier to your volume, review the Volumes screen for your current metadata size." when absolutely nothing on the Volumes page is labeled as "metadata".

Message 4 of 8
Xatosch
Apprentice

Re: RN516 with SSD on OS 6.9

All I have read about that is that it describes another senseless feature from netgear. It's only a hot topic in the whats new list, the same as ReadyDR, this was not a Desaster Recovery, more a DesasteR for me...

 

First I thought it was a HDD/SSD tiering, like Microsofts Storage Space it does and that I'm using since Windows 10 and that speeds up me PC with 3 WD Red and 2 SSD...

 

But only for MetaData? the log says I can use a 2 GB SSD... wow... what a benefit in a 10TB system...

Message 5 of 8
mdgm-ntgr
NETGEAR Employee Retired

Re: RN516 with SSD on OS 6.9

If you’re making lots of writes you’ll have a lot of metadata. There is metadata for every file and if you’re using CoW there will be metadata for every change to the file. For every change you make the system is going to write/update metadata. If you write the metadata to the SSDs (e.g. two SSDs in RAID-1) then this’ll improve performance.

If a SSD fails with two SSDs in RAID-1 you’ll have some protection against this.

 

For a 10TB volume you may well have single digit amount of GB of metadata. So not much needs to be written to the SSDs to improve performance.

 

With writes it’s not the large sequential writes that are slow with hard disks, it’s the smaller writes that are more “random” in nature that are slow. Metadata tiering is designed to provide maximum benefit for the use cases that will benefit the most from using SSDs.

 

Data Tiering would be something for the Ideas Exchange. Obviously for data tiering you’d benefit from higher capacity SSDs.

Message 6 of 8
Xatosch
Apprentice

Re: RN516 with SSD on OS 6.9

there is one thing you must remember, this is a NAS not a Server and low level NAS are for small business and home users as a graveyard for data, I don't think that are used with very high frequent access, more the transfer rates are important.

 

You are right, there is an advantage, but I think it's so small that I wouldn't buy 2 SSD's for it, no matter how small they are. And I have to sacrifice two slots for that little advantage.

 

> Data Tiering would be something for the Ideas Exchange.

 

I don't think so, because it will never be implemented, and when, then only in your high priced "data storage" models. Excactly the same why in OS6 it is not possible to adjust the block size for iscsi lun, only the data storage models have this option.

Message 7 of 8
kohdee
NETGEAR Moderator

Re: RN516 with SSD on OS 6.9


@Xatosch wrote:

I don't think so, because it will never be implemented, and when, then only in your high priced "data storage" models. 


Stay tuned.

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