On 9/16/21 9:23 PM, the Mulhern wrote:

Hi!

One thing I'ld like to mention is that in Stratis 3.0, you'll

be able to set the size of the filesystem at the command-line,

although the default size will remain 1 TiB. There are some caveats;

it's not a good idea to grow an xfs filesystem by more than about 8

times as the metadata layout is calculated for the original size specified.

So just for some clarity, if I had to make the rootfs smaller to make room for home to expand, would the only way to do that to be to wait for 3.0, then just re-create the FS with a smaller initial size? I don't anticipate it nearly growing past 8x the original size.

But, while this might be useful to others, I don't think it's really

all that relevant to your case. The amount of space allocated by the

thinpool for your data should really correspond to your filesystem

usage, which is only about 1 TiB.

Generally speaking, Stratis responds to devicemapper events, including

the low water event. It then does an analysis of your pool, including the

filesystems, to determine if any adjustment should be made.

Can you show us the output of the "stratis pool list" command? That

should show both the amount of space actually used (by your data +

Stratis metadata) the total size as understood by Stratis, and the amount

that Stratis interprets as free.

This is the output:

Name                       Total Physical   Properties                                   UUID
fedora   1.81 TiB / 1.06 TiB / 769.29 GiB      ~Ca, Cr   d9c81a12-b249-4c4c-ae7b-afe658911993

In case it helps, here's also the output of `fs list`:

Pool Name   Name          Used         Created             Device                            UUID                                
fedora      root_backup   125.42 GiB   Sep 05 2021 17:34   /dev/stratis/fedora/root_backup   4d2e3dc8-8b30-44f2-b2e9-d7be3f257784
fedora      home_backup   895.84 GiB   Sep 05 2021 17:33   /dev/stratis/fedora/home_backup   a96b7544-5047-461e-baee-f33311be9643
fedora      home          897.71 GiB   Sep 04 2021 22:54   /dev/stratis/fedora/home          80d9ffe8-f686-4c5c-9b2c-b9380d9a8309
fedora      root          122.97 GiB   Sep 04 2021 22:53   /dev/stratis/fedora/root          70398648-899d-426d-981f-313706768233

I...just realized I still have these snapshots lying around that I was (trying to) use for backup purposes, could that be affecting things as well?

From what you tell me, I think it's possible that, during I/O, the low water

mark is reset multiple times by stratisd, and also crossed multiple times,

triggering repeated re-evaluations of the pool and filesystem states, which

perhaps then result in no action, but cause the slow I/O that you mentioned.

You can't prevent Stratis from doing this check, without accepting a patch and

recompiling. This check is there to prevent running out of space, so it's

not optional. It is our present goal to make these checks more effective and less intrusive.

In fact, we just today merged a PR[1] which inaugurates

our development efforts on thinpool and filesystem management improvements.

Thanks for getting in touch,

- mulhern

[1] https://github.com/stratis-storage/stratisd/pull/2786

On Thu, Sep 16, 2021 at 8:45 PM Ryan Gonzalez <rymg19@gmail.com> wrote:

Hello there again! I've been using Stratis as my rootfs for a bit now,
and it seems to be working pretty well...with one particular catch...

For some context: I have a single 2TB pool on a single disk, with two
filesystems inside. When I created said filesystems, they seem to have
been both sized as 1TB, which was a bit confusing since I thought they
would start smaller and expand as I wrote to them. In particular, one of
them (the rootfs) is only ~200GB full, while the other is ~800GB. Of
course, the latter of these is reaching the current 1TB limit, which is
where things get...weird. In particular, based on the system logs, I
seem to have hit this:
https://github.com/stratis-storage/stratisd/issues/1466

 From what I can understand, this is just Stratis trying to expand the
filesystem. However...it doesn't seem to ever succeed, since the size
stays the same. Despite that, it still seems to run whenever I write in
a large amount of new data, resulting in some *very* brutally slow I/O
speeds (despite being on an NVMe disk), to the extent that I can't
really even open a terminal (to be fair, I have quite a few oh-my-zsh
plugins that could be contributing negatively to this...)

This has led to two particular questions:

- How exactly does the resizing of filesystems work? I know you can't
shrink XFS, but I believe the Stratis design paper references reclaiming
unused space via trims. Is it even possible for the rootfs to "shrink"
(but not really) to accommodate an expansion of the other one?

- If the other one can't expand, is it possible to just tell Stratis to
stop trying and avoid the major lag? Or, could there be something in my
configuration making this significantly slower than it's supposed to be
(maybe disk schedulers)?
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