Re: [SPDK] About mouting Blobstore and Lvolstore

* Re: [SPDK] About mouting Blobstore and Lvolstore
@ 2018-02-21  7:02 Zawadzki, Tomasz
  0 siblings, 0 replies; 9+ messages in thread
From: Zawadzki, Tomasz @ 2018-02-21  7:02 UTC (permalink / raw)
  To: spdk

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Hi Shuhei,

Just like Jim have mentioned:

-          blobstore (lib/blobstore) handles persistent allocation of data and metadata

-          lvol (lib/lvol) implements logic for creation of blobstore/blobs and managing relevant metadata (like lvs uuid, lvs name and lvol name)

-          vbdev_lvol (lib/bdev/lvol) exposes lvols via bdev layer

Please see http://www.spdk.io/doc/logical_volumes.html for description and RPC regarding lvols. After creation lvs and lvols are persisted on the device that they were created on.

As soon as that device is added to SPDK, it is examined for lvol store presence - if it’s there, it’s loaded.
This examine process is generic for bdev. When spdk_bdev is registered, examine callback is issued for all bdev types that assigned it. At this time this mechanism is used by lvols, GPT, split and error.
For details please see functions like _spdk_bdev_register(), SPDK_BDEV_MODULE_REGISTER and specifically for lvol - vbdev_lvs_examine().

For example from RPC point of view. As soon as NVMe device is added (construct_nvme_bdev RPC) and it contained lvs with lvols, they are immediately exposed as bdevs. Just like they were before previous SPDK instance run was closed.

Thanks,
Tomek

From: SPDK [mailto:spdk-bounces(a)lists.01.org] On Behalf Of ???? / MATSUMOTO,SHUUHEI
Sent: Wednesday, February 21, 2018 1:43 AM
To: Storage Performance Development Kit <spdk(a)lists.01.org>
Subject: Re: [SPDK] About mouting Blobstore and Lvolstore

Hi Jim,

We have discussed that JSON config file may be better to be a list of JSON RPC request first.

However for lvol and lvolstore, metadata and data are already persistent in the blobstore.

Hence JSON config file will not be direct solution.

If I understanding correctly, the implementation that lvol and lvolstore are automatically made available when mouting may be the way many hope.

Please revise me if my understanding is wrong.

Thanks,

Shuhei

________________________________
差出人: SPDK <spdk-bounces(a)lists.01.org<mailto:spdk-bounces(a)lists.01.org>> が 松本周平 / MATSUMOTO，SHUUHEI <shuhei.matsumoto.xt(a)hitachi.com<mailto:shuhei.matsumoto.xt(a)hitachi.com>> の代理で送信
送信日時: 2018年2月21日 9:19
宛先: Storage Performance Development Kit
件名: [!]Re: [SPDK] About mouting Blobstore and Lvolstore

Hi Jim,

Thank you but my question might not be clear.

What I would like to know is that how to ensure that each LVOL is attached to the same blobstore and blob after rebooting.

The name of lvol_bdev is returned by creation and is lvolstore_uuid + blob_id.

However I have not seen any code to use the name of lvol_bdev for lvol creation.

If the name of lvol_bdev is used to allocate lvol to blob, the same blob will be ensured to be allocated.

Do you have any good idea or the solution is already implemented about how lvol library satisfies the responsibility?

I hope this make sense to you.

Thanks,

Shuhei

________________________________
差出人: SPDK <spdk-bounces(a)lists.01.org<mailto:spdk-bounces(a)lists.01.org>> が Harris, James R <james.r.harris(a)intel.com<mailto:james.r.harris(a)intel.com>> の代理で送信
送信日時: 2018年2月21日 9:09:02
宛先: Storage Performance Development Kit
件名: [!]Re: [SPDK] About mouting Blobstore and Lvolstore

Hi Shuhei,

Blobstore is meant as a generic persistent block allocator.  Lvolstore is an SPDK logical volume implementation based on Blobstore to present blobs as a block device.  Blobfs is a minimal SPDK filesystem based on Blobstore to present blobs as files.  So for purposes of library dependencies - both lvolstore and blobfs depend on Blobstore.

Regarding “mounting” a logical volume - the lib/bdev/lvol library is responsible for presenting logical volumes as SPDK bdevs.

Regards,

-Jim

From: SPDK <spdk-bounces(a)lists.01.org<mailto:spdk-bounces(a)lists.01.org>> on behalf of 松本周平 / MATSUMOTO，SHUUHEI <shuhei.matsumoto.xt(a)hitachi.com<mailto:shuhei.matsumoto.xt(a)hitachi.com>>
Reply-To: Storage Performance Development Kit <spdk(a)lists.01.org<mailto:spdk(a)lists.01.org>>
Date: Tuesday, February 20, 2018 at 4:02 PM
To: "spdk(a)lists.01.org<mailto:spdk(a)lists.01.org>" <spdk(a)lists.01.org<mailto:spdk(a)lists.01.org>>
Subject: [SPDK] About mouting Blobstore and Lvolstore

Hi All,

I'm investigating the dependency relationship among SPDK libraries and subsystems mainly for JSON configuration management.

I understand that blobstore manages metadata persistently.

However I have not found anything about mouting blobstore or lvolstore in  source code, Trello, or document yet.

Mouting in this case means a process by which SPDK makes lvolstore and lvol on disks available for user to access via virtual bdev.

Am I missing something or have I totally misunderstood?

Otherwise mounting function is great to have for us?

This question is only from code and document reading.

I'm not confident in my understanding yet and I would appreciate for your any feedback.

Thanks,

Shuhei

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