Difference between "static volumes" and "thick volumes"

[sjakub]

Hi.

Does anybody know what the difference between static volumes and thick volumes is?
It looks like both use LVMs. Static volumes are described as having the "best performance",
while thick volumes (on a storage pool) have "good performance".

I would like to understand what are the pros and cons of both options, but I haven't found anything helpful.
There is one topic that discusses something similar: http://forum.qnap.com/viewtopic.php?f=25&t=101473
with comments saying that storage pools are an improvement and people should want them.
But I would really like to know *why*...

I tried setting up both, and both give me options to add RAID groups (either to the storage pool or to the volume),
or expand existing RAIDs with additional disks (unless, sadly, for RAID 10 is used).
One difference that I noticed is that when I create a storage pool and thick volume, I perform operations
from "storage pool" screen, while when I create a thick volume, I have to use "volumes" screen - but it looks
like both offer similar functions.

Another difference is that since I don't have a storage pool, I cannot create additional volumes.
And that difference is not relevant if I only want to have a single volume.
Also, I don't see how that would affect performance (in both cases LVM is used)...

And, before someone starts talking about thin provisioning,
I am trying to determine differences between "thick" volumes and "static" volumes.

[AdrianW]

Have a read of this thread: Do home users have a use/need for Storage Pools?

Even though I ended up using a Storage Pool - I can't actually see any benefit over a static volume if you're creating a single volume.

[sjakub]

Yes, I've read it. That's the one I mentioned (and linked) in my post.
However, there is no actual explanation what the differences or trade-offs are...

[AdrianW]

Yes, I've read it. That's the one I mentioned (and linked) in my post.
However, there is no actual explanation what the differences or trade-offs are...

Doh! I completed missed your link.

No one, at least on this forum, seems to be able to explain the differences properly.

I'd previously asked basically the same question here, and got no reliable answer.

I did find this article which explains storage pools - but it still doesn't really help in making a decision on which to use.

[schumaku]

QNAP originally introduced the "Static Volume" with the initial launch of the TS-x51/TS-x53/TS-x53S series - in the aim to offer a plain simple volume management, similar to what we have on the NAS with the "legacy" volume manager. Since 4.1.2, this "Static Volume" option became available on all newer NAS models with the new storage manager.

No one, at least on this forum, seems to be able to explain the differences properly.

Because it's a new selection option - for certain NAS models (see above) it was - for some NAS models (ie. TS-x31 Plus) it still is the only choice.

The Volume Creation Wizard says:

QTS_4.1.2_20141229_create_volume_wiz.JPG

All differences are explained here. What is unclear please?

[AdrianW]

All differences are explained here. What is unclear please?

I would expect most home users would be creating a single volume comprised of all of their installed disks.

What is not clear is why I should choose a storage pool with a single thick volume over a static volume. That screen shot says a Static Volume has the best performance - so it would seem that if all you want is a single volume using all your disks you should choose Static Volume.

Thick volume apparently gives you flexibility - but with a single volume I can't see what flexibility it is providing.

Patrick keeps saying in various threads that storage pools are an improvement and that you should "want them". But why? What is the actual benefit? (to someone who only wants a single volume).

And thin volume seems to make no sense at all - but that's another story. (I can't see the point in pretending you have more space than you actually do).

[schumaku]

I would expect most home users would be creating a single volume comprised of all of their installed disks.

Probably yes, probably no. But that's why the Static Volume feature was made available, indeed.

What is not clear is why I should choose a storage pool with a single thick volume over a static volume

Because they start with a smaller number of HDD today, say two 4 TB (because of costs), and plans to buy the next pair when the larger capacity HDD (say two 6 TB) when the prices are in the "linear" range, and you want to bring these two RAID1 into the same volume in a Storage Pool for example.

Patrick keeps saying in various threads that storage pools are an improvement and that you should "want them". But why? What is the actual benefit? (to someone who only wants a single volume)

Not convinced we are all talking of the same here.

The point it that we both don't suggest to migrate legacy volumes to new NAS models supporting the new storage manager! This translated to using the fully fledged storage manager on most "SMB" NAS.

What is named Static Volumes was (implicitly) the default on the TS-x51/x53 at market launch with 4.1.1, and it's the only one for newer entry level system like the TS-x31 Plus - no other NAS model with the Flexible Storage Manager had this feature available.

Things have somewhat changed with 4.1.2 - all NAS with the Flexible Storage Manager have got the Static Volume option. As per the release notes, TS-x51/x53 got the option to combine multiple Static Volumes into a Storage Pool.

Even with a large playground of test NAS, it's hard to keep all these changed features under tested - time and resources is simply limited.

[AdrianW]

Because they start with a smaller number of HDD today, say two 4 TB (because of costs), and plans to buy the next pair when the larger capacity HDD (say two 6 TB) when the prices are in the "linear" range, and you want to bring these two RAID1 into the same volume in a Storage Pool for example.

But you can do that with a static volume as well (can't you?). Say, if you started out with 3 drives in RAID 5 and then added a 4th to the array.

[schumaku]

Say, if you started out with 3 drives in RAID 5 and then added a 4th to the array.

Of course - but you can't get an advantage if adding _bigger_ drives to the ones installed. If adding a 6 TB HDD to the 3 * 4 TB RAID5 you win 4 TB - or loose 2 TB.

Say you have a six bay, you can run 3*4TB RAID5 and add 3*6TB RAID5 to the same storage pool - the same volume.

While talking on this example, please note you can't add a non-redundant single HDD, RAID0, ... volume to a storage pool containing a redundant storage.

I can't see any major drawback of using the flexible storage manager - if really required with a thick allocated volume.

The thing with the thin allocated volumes is that things must be dynamically extended if adding data - when data is removed, the space will be freed up again (nightly job) - this does create some performance overhead.

edit: typo

[sjakub]

I played a bit with it, and even when I create a static volume there is an option to extend underlying RAID
group by adding new drives to it, as well as to add a completely new RAID group
(which should allow to take advantage of different disk sizes...).

The only difference that I can see is that if I create a static volume,
I cannot add more volumes to the same RAID group/groups (essentially "internal" storage pool).
But in both cases it looks like LVM is used.

So where would the performance difference ("best performance" vs "good performance") come from?

[schumaku]

When we go the the bigger picture, all newer NAS models are based on the same Storage Manager, able to replace the "legacy" storage manager we're used to since QNAP v2 and v3.

when I create a static volume there is an option to extend underlying RAID group by adding new drives to it

Yes, this is a basic functionality for all new Storage Manager feature sets.

as well as to add a completely new RAID group

Yes, another basic functionality for all new Storage Manager feature sets.

(which should allow to take advantage of different disk sizes...).

Correct - the standard RAID1/5/6/10 limitations apply per RAID group.

The Storage Pool feature is not available on feature sets - this does permit permitting to combine multiple RAID groups into a single volume.

At product launch, the TS-x51/x53 models only have got Static Volumes, and no Storage Pool. The 4.1.2 build 1229 release notes say - "Adds support for multiple RAIDs in a storage pool (For TS-x51/x53 models only.)" ... so that's why it's possible on your NAS model now.

The only difference that I can see is that if I create a static volume, I cannot add more volumes to the same RAID group/groups (essentially "internal" storage pool).

Hm, some more - essentially correct for the pure storage.

But in both cases it looks like LVM is used.

This why I wondered why QNAP has chosen this approach - and Static Volumes can't be changed to Thick Volumes.

So where would the performance difference ("best performance" vs "good performance") come from?

I don't have comparisons at hand - can't be much of a difference. Probably made to keep typical consumers away from the complex stuff.

[williamjames07]

i have no idea about this.

[sjakub]

If anybody else is interested in this, I did some tests.

First of all, it looks like "static volumes" use "traditional" LVM.
Logical volume on a volume group of physical volumes.
The limitation (I think it's just QNAP's, not LVM's)
is that there is only one volume per group of disks.

When storage pools are used, LVM is configured differently,
in a way that allows thin or thick volumes to be created.
This makes it possible to have several different volumes
on a single RAID group.

However, it looks like using pools has performance implications.

I run some simple tests - reading and writing (several times)
20 gigabytes of data using either small (1KB) blocks,
or large (1GB) blocks.

I did this with no other load on the system and using different
volume configurations.

For a single disk volume (which should represent a "base"
performance of a single disk) I was achieving 128 MB/s writing
and 160 MB/s reading speed with small blocks,
and 153/160 MB/s with large blocks.

All other tests were performed using different RAID groups with either
static volumes or thick volumes on a storage pool - all with 4 disks.
The tests were performed after the file system finished "optimizing"
and once the array synchronization was finished.

The next configuration was RAID 10 and static volume.
I was getting 131/323 MB/s with small blocks, and 247/323 MB/s with large blocks.

RAID 10 with a storage pool gave me following numbers:
123/344 MB/s (small blocks) and 174/345 MB/s (large blocks).

RAID 6 and a static volume: 126/76 and 168/73

RAID 6 and a storage pool: 123/75 and 160/72

RAID 0 and a static volume: 134/530 and 295/569

And, finally, RAID 0 and a storage pool: 131/311 and 272/298

Also, both RAID 10 and RAID 6 took significantly longer to synchronize after creating
thick volumes - about 26-27 hours with storage pools compared to 13-16 hours in "static volume" configuration.

So it looks like in almost all cases storage pools made things slower.
I'm not sure, however, why RAID10 read speeds were slightly higher.
I run everything again to check those cases, but results were consistent.
In all the other cases storage pools, for some reason, make both writing and reading consistently
(and sometimes, depending on the RAID, significantly) slower.

Also, RAID6 was significantly slower to read data - it was getting half of the read speeds of a single drive!

I am not claiming those are professional tests, and they most likely could be done better.
I was simply curious to see what I could expect from different volume configurations.

Also, I experimented with volume expansion. And it looks like static volumes can be extended in
a similar way to storage pools - by adding additional disks to the RAID group
(sadly, this doesn't work with RAID10). But they also allow to be extended by adding new RAID groups
to the same volume - of the same or different RAID level. I was actually able to create
a static volume on a two disk RAID 0 array, and later extend it with a new 2 disk RAID 1 array.
Not that configuration like that makes much sense... But it worked!

Given the results, the fact that I only need a single volume per RAID group
and that I don't need snapshots or thin volumes, I am going to stay away
from storage pools (and RAID 6 as well).

In addition to better performance, static volumes use simpler underlying LVM configuration.
I don't know much about LVM pools and I am not claiming that there is anything
wrong with them, but I like to keep things as simple as possible.

[AdrianW]

@sjakub - thanks for that useful info.

I'm using RAID 6 in a storage pool - so even though your read speeds are strangely low - there's hardly any difference between storage pool and static volume:

* RAID 6 and a static volume: 126/76 and 168/73
* RAID 6 and a storage pool: 123/75 and 160/72

I'll have to check the read speed on mine to see what I'm getting.

[sjakub]

Yes, with RAID 6 they are very close. But even though they are this close, the speeds with storage pool are consistently lower.