Glossary
Account
Section titled “Account”A named identity in the admin server that owns volumes and authenticates with an account token. Enterprise only.
A fixed-size chunk of file data stored in object storage. The block size is configured per volume (256 KiB to 8 MiB, default 4 MiB).
Block API
Section titled “Block API”The storage protocol used to access a block store. Supported values: s3, gcs, azure, oci.
Block Store
Section titled “Block Store”A configured object storage location (bucket + optional prefix) where flexFS writes block data. Each block store is associated with a provider and region.
An estimated monthly storage cost in US dollars ($/month), computed per file as (effective_size / 1 GiB) * rate. The effective size is the smaller of the file’s logical size and its allocated size (block size times the number of allocated blocks), protecting sparse files from overcharging. The rate is a per-GiB monthly dollar amount determined by the file’s size bin — an activity-based tier. Rate bins are configured per account and allow tiered pricing by data temperature. Reported by analyze.flexfs and find.flexfs.
CSI (Container Storage Interface)
Section titled “CSI (Container Storage Interface)”An industry standard for exposing storage to container orchestrators. csi.flexfs implements CSI to provide flexFS volumes to Kubernetes pods.
Dentry
Section titled “Dentry”A directory entry — a name-to-inode mapping within a directory. Dentries are stored in the metadata server, and the mount client caches recent lookups to avoid repeat round trips.
FUSE (Filesystem in Userspace)
Section titled “FUSE (Filesystem in Userspace)”A Linux kernel interface that allows filesystem implementations to run in user space. FlexFS uses FUSE3 to present volumes as local filesystems.
A metadata record describing a file, directory, symlink, or special file. Contains attributes such as size, ownership, permissions, and timestamps.
Meta Store
Section titled “Meta Store”A registered metadata server instance in the admin server’s configuration. Linked to volumes to route mount clients to the correct metadata server.
Mount Path
Section titled “Mount Path”The subdirectory within a volume that a volume token restricts access to. When set, the mount client sees only the subtree below that path.
Provider
Section titled “Provider”A cloud or custom infrastructure provider (e.g., aws, gcp, azure, oci). Providers are registered in the admin server and used to organize regions and block stores.
Proxy Group
Section titled “Proxy Group”A set of one or more proxy servers that cache block data for a region. Mount clients select the lowest-latency group using RTT probing and distribute blocks across group members using rendezvous hashing. Enterprise only.
Region
Section titled “Region”A geographic or logical zone within a provider (e.g., us-east-1). Regions group block stores and proxy groups by location.
Rendezvous Hashing
Section titled “Rendezvous Hashing”A consistent hashing algorithm used by mount clients to distribute blocks across proxy servers within a group. Each block is deterministically assigned to a specific proxy without requiring a central lookup.
Retention
Section titled “Retention”The duration for which deleted data (both metadata and block data) is preserved, enabling time-travel mounting. Configured per volume; -1 means forever. Default is 7 days.
Secret ID
Section titled “Secret ID”An identifier for the end-to-end encryption key material registered with the admin server. Used to verify that mount clients provide the correct secret when mounting encrypted volumes.
Rate Bin
Section titled “Rate Bin”A mapping from size bin number to a per-GiB monthly dollar rate ($/GiB/month), configured per account. Rate bins enable tiered storage pricing: recently-active data can be priced differently from cold data. The cost computation walks backward from a file’s size bin to find the applicable rate. Used by analyze.flexfs, find.flexfs, and the statistics server for billing.
Size Bin
Section titled “Size Bin”An activity tier reflecting how long since a file’s data was last used. Each ~30-day step (bin 0 = active within the past 30 days, bin 1 = 30-60 days ago, and so on, up to bin 127) is a higher bin, and rate bins can price colder tiers differently. Reported as size_bin by find.flexfs, and as the last_active column by analyze.flexfs --friendly. See the Billing Model for how tiers are priced.
A file’s tier is determined by I/O on its data: opening it for reading, and reading, writing, truncating, or extending it. Metadata-only operations do not count, so listing a directory, running stat, chmod, or touching a file does not warm it, and neither does setting its timestamps by hand. Mounts report this I/O to the metadata server; for a mount that does not report activity, the server derives it from the requests that I/O produces. A file whose data has not been used since the metadata server began recording activity is placed by the most recent of its access, modification, and creation times, so a file copied in with old timestamps starts no colder than the copy itself.
The tier is sticky by design: it advances only once a file’s use is sustained (a single backup or indexing pass does not warm it), and timestamps set by hand are ignored in either direction, so a file cannot be moved to a cheaper tier by rewinding them or to a more expensive one by a bare touch. Within the hottest tier every use simply refreshes the file, so a file that falls quiet after steady use still gets one free pass before it is repriced.
Volume
Section titled “Volume”A logical filesystem managed by flexFS. Each volume has its own namespace, block store, metadata store, and configuration (block size, compression, end-to-end encryption, retention).
Volume Token
Section titled “Volume Token”A UUID that grants access to a specific volume. Volume tokens can be scoped to a mount path (subdirectory) and carry per-token mount flags. Mount clients authenticate using a volume token.
XACL (Extended ACL)
Section titled “XACL (Extended ACL)”A POSIX.1e access control list that extends standard Unix permissions (owner/group/other) with per-user and per-group entries. Stored as extended attributes (system.posix_acl_access and system.posix_acl_default). Enabled with the --acl mount flag.
Xattr (Extended Attribute)
Section titled “Xattr (Extended Attribute)”A name-value pair associated with an inode, extending the standard POSIX attribute set. Used by ACLs, SELinux labels, and user-defined metadata.