Introduction
A HSM (Hierarchical Storage Management) provides
- (nearly) unlimited storage space and
- two replicates on tape (in different buildings for security)
- a third copy on disk (for selected data, smaller files for faster access) → VTL (Virtual Tape Library, Silent Brick)
However, there are two caveats:
- Your (larger) Data is archived on a tape, so it will take a while to get it back (unless it is online or has a disk-copy).
- You need a project to archive your data (apply for a project here: eResources).
HSM at AWI
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Concept
Principle Idea
- HSM: A (H)ierarchical (S)torage (M)anagement system consists of (at least) two storage systems: A cache speeds up access, and the hierarchy reduces cost. Based on a set of rules, data is stored on certain connected storage devices (tapes and optional disks).
- ScoutFS is used at AWI since 2024 and supersedes samfs (used since decades before) www.versity.com/products/scoutfs/ www.scoutfs.org .
- ScoutAM is used as (A)rchive (M)anager www.versity.com/products/scoutam/ and supersedes OHSM/VSM
The Circle of Life
Archiving
- When creating a file in ScoutFS (e.g., by rsync, scp, ftp, S3-PUT) the data is stored on a fast SSD cache system.
- Depending on predefined policies (e.g., when the file has not been modified for a specific amount of time) the file is automatically archived on slower (and much cheaper) tapes (and optionally HDD).
- A file just created is online
Releasing
- The metadata (filename, size, ownership, permissions, etc.) of a file remains always in the cache system and is visible/accessible, but
- when the cache system fills up (e.g, 90% capacity) the data of large files and files that have not been touched for some time is released.
- If the data of the file is released it is called offline.
- The user does (in the first instance) not see any difference between an online and an offline file.
Staging
- When offline data is accessed ScoutAM intercepts the call and automatically gathers the data from the archive media. ScoutAM uses information stored in metadata to find (and stage = "copy back") the data.
- In the meantime the read from this file is blocked, thus the process accessing the data blocks is blocked, too.
- When accessing more than a few files, prior staging is strongly recommended (see User commands)!
Recycling
- If the content of a file changes a new archive copy has to be produced. (You can not modify just the relevant bits on the tape.)
- The previous archive copy becomes useless (aside from having an additional backup of a previous version).
- If a file is deleted, the archive copy becomes useless, too.
- Both processes result in unused (invalid) sections on a tape.
- Eventually only a small part of a tape contains relevant (up to date) information. The residual data can be archived on other tapes, the old tape is erased and can be used for future archive copies. This process is called recycling.
Hardware
Tape Library
- 2 TFinity Tape Libraries in two buildings
- each has 3100 licensed slots for LTO tapes
- 600 LTO-9 tapes in each library (600x ~20 TB → ~12 PB)
TFin-E |  TFin-D |
Server, Switches and disks
- Three Dell R760xd server ( hssrv2[a-c] )
- 4 Brocade (32Gb) 6610 SAN switches
- 270 TB SSD primary cache (Dell ME5084)
- 488 TB extended HDD-cache (Dell ME5084)
- Ab Ende 2024:
1120 TB Virtual Tape Library (VTL) Silent Brick von Fast-LTA- Controller G5200
- SAS Switch
- 7x SilentBrick Max