Used for Protection

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Used for Protection

Joseb

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In using Synolog's online RAID Calculator I see that if I were to say fill a DS1019+ for example, with five 6gb drives, that I would end up with 24GB of space on the combined four drives and that one 6GB drive would be "Used For Protetion". I guess that "Used for Protection" is another way of saying that all that's in the 24GB of space is on the 6GB of the Used For Protection Drive ? Is that what it means. And if so, how does 6GB hold 24GB of data? Is is compressed?
 
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Hi,

I believe you were looking at the calculator options for SHR/RAID 5.
It‘s not saying that one of the 6TB drives is used for protection. It’s saying that 6TB of the total space of all those drives is used for protection.

It‘s distributed. So if any disk of the five fails (in an SHR/RAID 5 configuration), the NAS still runs degraded until you replace the failed disk.

And you’ll be using TB not GB drives.

SHR/RAID uses parity for protection.
 

fredbert

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And if so, how does 6GB hold 24GB of data?
It's some complicated maths. This is the gist of it but don't ask me to implement it using this explanation :) :

You take the same block on each of the 4 disks and combine them to calculate a parity block. If one of the 4 main blocks fails then using the remaining 3 blocks plus parity block you can do another calculation and infer the value of the failed block.

When one disk fails it only takes away the main data blocks it holds, plus and parity blocks. The remaining disks work harder to provide any data that was on the missing disk and again when a replacement is inserted and a rebuild is happening.
 

Joseb

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Thanks for the explanations! I appreciate it.
 
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For (5) 5TB drives (I'm using 5TB in this example to make the math clearer)... SHR/RAID5... each drive contains 4TB of data and 1TB of parity protection.

When one drive fails, you "lose" 4TB of data.

When you insert a new replacement drive, that 4TB of "lost" data is recovered from the remaining 4 drives (each contributing 1TB from its "protection" data).

It matters not which drive dies, the other 4 have sufficient information to reconstruct the "missing" data.

The example is a simplistic picture of what happens, illustrating how each disk is "protected" by the others.
 

Joseb

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Thanks Telos. I guess that all the drives have about 1/4 of all the other drives data. Probably more complicated than that. But as long as it works it's great. I am debating getting the DS918+ or the DS1019+. The only thing for me to figure out now is do I want the ability of having two drives fail and recover (DS-1019+) or take the chance that one drive will fail and buy the DS918+? I don't know the failure rate of these things. Thanks again.
 
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The only thing for me to figure out now is do I want the ability of having two drives fail and recover (DS-1019+) or take the chance that one drive will fail and buy the DS918+?

For me, the number of disks (4 or 5) doesn't enter into the level of redundancy decsion. Personally, I would not use SHR2/RAID6 on a personal NAS with 4-5 disks. But even if you choose to, you will still need a NAS-independent backup plan. Disk redundancy is not a substitute for backup.

In my circumstances, I would go with the 1019+, with 4 disks in a common SHR pool (4x8TB), leaving a slot open for expansion. But my circumstances aren't your circumstances. Whatever you decide will work. This is no wrong answer.
 
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If you’ve just got your 218+ and you’re not outgrowing it already (not only storage wise but capabilities wise too), I’d suggest that you wait.
Use it and understand the various configurations, features and capabilities (and limitations). You’ll be in a better position to make your second purchase more useful for your (discovered) needs. Or you may find that what you have is good enough and there’s no need to buy anything now.

SynoForum is a good place to learn. Check the resources section, use the search function and of course you can ask anytime.

However, if you must buy now, go for 920+ for a four bay (not 918+) or a 1019+ for a five bay.

The last two digits in Synology’s model numbers denote the year of introduction. The first digit(s) are the maximum number of bays supported (sometimes with an expansion unit).

A 1019+ was introduced in 2019, can support a maximum of 10 bays (with the optional 5 bays unit connected) and it’s a plus series.
 

Joseb

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For me, the number of disks (4 or 5) doesn't enter into the level of redundancy decsion. Personally, I would not use SHR2/RAID6 on a personal NAS with 4-5 disks. But even if you choose to, you will still need a NAS-independent backup plan. Disk redundancy is not a substitute for backup.

In my circumstances, I would go with the 1019+, with 4 disks in a common SHR pool (4x8TB), leaving a slot open for expansion. But my circumstances aren't your circumstances. Whatever you decide will work. This is no wrong answer.
For me, the number of disks (4 or 5) doesn't enter into the level of redundancy decsion. Personally, I would not use SHR2/RAID6 on a personal NAS with 4-5 disks. But even if you choose to, you will still need a NAS-independent backup plan. Disk redundancy is not a substitute for backup.

In my circumstances, I would go with the 1019+, with 4 disks in a common SHR pool (4x8TB), leaving a slot open for expansion. But my circumstances aren't your circumstances. Whatever you decide will work. This is no wrong answer.

Thanks Telos, I will seriously take your advice. Again, thanks for getting back to me.
 

Joseb

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If you’ve just got your 218+ and you’re not outgrowing it already (not only storage wise but capabilities wise too), I’d suggest that you wait.
Use it and understand the various configurations, features and capabilities (and limitations). You’ll be in a better position to make your second purchase more useful for your (discovered) needs. Or you may find that what you have is good enough and there’s no need to buy anything now.

SynoForum is a good place to learn. Check the resources section, use the search function and of course you can ask anytime.

However, if you must buy now, go for 920+ for a four bay (not 918+) or a 1019+ for a five bay.

The last two digits in Synology’s model numbers denote the year of introduction. The first digit(s) are the maximum number of bays supported (sometimes with an expansion unit).

A 1019+ was introduced in 2019, can support a maximum of 10 bays (with the optional 5 bays unit connected) and it’s a plus series.
Excellent! Good to know. I have decided to wait, research and save my pennies. You have all been great.
 

Joseb

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Personally, I would not use SHR2/RAID6 on a personal NAS with 4-5 disks.

In my circumstances, I would go with the 1019+, with 4 disks in a common SHR pool (4x8TB), leaving a slot open for expansion. But my circumstances aren't your circumstances. Whatever you decide will work. This is no wrong answer.
Now I am curious. What would you use in a 4 or 5 bay NAS. Which RAID? And if you have time, why?
 
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Now I am curious. What would you use in a 4 or 5 bay NAS. Which RAID?
I would choose SHR for data storage/streaming. If I was also using a surveillance package, I might go with an alternate RAID type alongside the SHR.

IMO SHR2 use borders on paranoia for a small NAS (please no offense as we each have different risk tolerances which shape our decisions). If I were running a business that required 24/7 uptime I might consider SHR2 (or RAID10). But SHR2 is a performance dog (my opinion here) and a capacity drag. With a solid backup plan, and decent drive hardware (NAS/Enterprise-rated drives... not something I shucked from a WD Elements sale), SHR is a solid performer.

I've never heard a personal NAS user say... I wish I had chosen SHR2... but I've often heard the opposite.
 
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Now I am curious. What would you use in a 4 or 5 bay NAS. Which RAID? And if you have time, why?
As @Telos said. It gives you more flexibility to play with the configuration.

Initially I was waiting for the release of the 920+, but after a long consideration I decided to go with the 1019+ Because it allows me to do what I want with SHR in a more economical way.

With the 1019+, I have two drives configured in a single pool with SHR-1 (mirroring) with Btrfs file system (just like your 218+), while the remaining 3 are configured in SHR-5 pool with ext4 file system.

The two mirrored drives are for my important stuff, while the the other three are for media files and the likes.

If I had gone with a 920+, one option (among others) if I want to maintain the above split is to have two mirrored and the remaining two also mirrored. Mirroring is very expensive. Having that extra bay with the 1019+ allowed me to stretch the storage capacity with SHR-5 (requires a minimum of three drives). Of course, one can go with all in an SHR-5 configuration or any other possible configuration. It’s your choice. There’re advantages and disadvantages to each. It’s all up to you at the end :)
 

Rusty

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I use RAID5 with 3-4 drives, and raid6 with my 12 bay configurations. Also there is a mix of RIAD1 and RAID0 depending on the needs.

So all in all as it was already said, it comes down to total capacity and backup that will in the end determine do you need and what kind of redundancy.
 

Joseb

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I use RAID5 with 3-4 drives, and raid6 with my 12 bay configurations. Also there is a mix of RIAD1 and RAID0 depending on the needs.

So all in all as it was already said, it comes down to total capacity and backup that will in the end determine do you need and what kind of redundancy.
Thanks Rusty. I better read more about all these raid configurations.
 

Rusty

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Thanks Rusty. I better read more about all these raid configurations.
Keep in mind that SHR is RAID5 and SHR2 is RAID6. SHR is syno version of raid types that unlike the conventional RAID types offer a mix of different size drives in order to utilize max space. RAID0 is a combination of multiple drives into a single large volume with no redundancy at all (meaning one drive in the volume is damaged you lose all your data). RAID1 is a mirror. So with 2 drives, you love half the space for redundancy, but in case that ether drives fails you still have all your data safe (on the other, mirrored drive).

Also, RAID is not backup, this is just redundancy so you can keep going.
 

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