[LU-11829] Separate the naming structure between RW-PCC and RO-PCC

• Status: Open
• Project: Lustre
• Type: Technical task
• Priority: Minor
• Reporter: Qian Yingjin
• Assignee: Qian Yingjin
• Resolution: Unresolved
• Labels: PCC

Description

Currenly a PCC backend can provide caching services for both RW-PCC and RO-PCC which both use lhsmposix naming structure as follows:

 "%04x/%04x/%04x/%04x/%04x/%04x/" DFID_NOBRACE

However, sharing the same naming structure may cause some confusions. For example, when RO-PCC cache a HSM archived file (not HSM released), it may confuse the user that whether the cached file object in the PCC device is RO-PCC cached file or a HSM archive. Moreover, a HSM remove request maybe delete the RO-PCC cached file wrongly.
To solve this problem, we add a suffix .rdonly for RO-PCC naming strcuture to distingush from the RW-PCC and HSM solution:

"%04x/%04x/%04x/%04x/%04x/%04x/"DFID_NOBRACE".rdonly"

Comments

[Andreas Dilger]

Note also that the current lhsmtool_posix naming convention for objects is not very good, and should be avoided for new deployments. It currently puts the low part of the FID at the top of the directory tree, and the high part of the FID in the lower directories. This means that each directory leaf will only ever have a single filename in it until many billions of files are archived.

Instead, the naming should be changed to do the opposite - put the high word of SEQ at the top of the directory tree, and the low word of the OID at the bottom. This will keep some reasonable number of objects in each leaf directory (eg. 65000) and keep a more compact directory tree.

If this needs a change to the POSIX copytool, then for compatibility it should create a config file or marker at the top of the tree (eg.lhsm_posix_v2) and check for that at startup to determine if the new naming format should be used or the old one.

[Qian Yingjin]

Hi Andreas,

Thanks for you comments.

I think we should create a new ticket to discuss and improve the usage efficiency of the current lhsmtool_posix naming convention for objects.

 

Regards,

Qian

[Gerrit Updater]

Yingjin Qian ([e-mail]) uploaded a new patch: https://review.whamcloud.com/33942
Subject: LU-11829 pcc: Separate the naming between RW-PCC and RO-PCC
Project: fs/lustre-release
Branch: pcc
Current Patch Set: 1
Commit: 4e0acfaf9d892db32da4fa99dc2665f8e28ac979

[Gerrit Updater]

Yingjin Qian ([e-mail]) uploaded a new patch: https://review.whamcloud.com/38309
Subject: LU-11829 pcc: Use different fnames for RW-PCC and RO-PCC modes
Project: fs/lustre-release
Branch: master
Current Patch Set: 1
Commit: dff3b6ab81c8e11cf79e4f67447fc884c7747aa5