Keep storage classes » History » Revision 12
Revision 11 (Tom Clegg, 06/14/2017 01:05 PM) → Revision 12/15 (Tom Clegg, 11/29/2017 08:37 PM)
h1. Keep storage classes groups h2. Use cases * Partition data among several cloud buckets for legal or financial reasons. * Shift data from "hot" to "cool" storage (e.g. SSD to disk) for price/performance tradeoff. * Move data from on-line to off-line storage (e.g. Glacier) but maintain provenance. h2. Requirements * arv-put & arv-copy have option to specify storage class. group. ** When writing each block, client can specify storage class group for the block. ** Use API to specify that the blocks belonging to a collection should go into a certain storage class. group. * Workbench permits changing storage class group on a collection * arvados-cwl-runner has options to specify storage classes groups for intermediate and final output collections. ** Use API to specify the storage class group for the output collection of a container request. * TBD: access controls on storage classes, groups, can restrict which users can place collections in which storage class? group? * TBD: rules for de-duplicating blocks across classes? groups? (e.g., if collections with identical data exist in "hot" & "cool" classes, groups, do we really need a copy of the data in "cool" as well as the copy in "hot"?) h2. Design A "storage class" group" is effectively a tagging scheme to specify a group of keep volumes servers (& volumes/mounts of a keep server) where a block should be preferentially stored. Generalized from [[Keep storage tiers]] (but unlike storage tiers proposal, there is no implied price/performance relationship between classes). groups). Each keepstore service has access to one or more storage classes. groups. Storage classes groups are independent. Data assigned to a class group may still be sharded among multiple servers. Classes Groups are be identified with labels or uuids instead of integers. The keep services table adds a column which lists which classes groups are available at which services. When writing blocks, keepstore recognizes a header @X-Keep-Storage-Classes@ @X-Keep-Storage-Group@ and accepts or denies the block based on whether it can place the block in the designated classes. group. If not supplied, keepstores should have a default pool. The value of @X-Keep-Storage-Classes@ @X-Keep-Storage-Group@ should be reported in the response. Each keepstore volume (mount) is associated with a number of storage classes. group. Collections may specify a desired set of classes group for the blocks in the collection. Keep balance should move blocks to volumes that offer the desired classes. group. If multiple collections reference the same block and in different sets of classes, multiple copies may be required. group, each group should have a copy with full replication. Data management policies, such as "move data from hot storage to cool storage after 1 month", should be implemented on top of the keepstore layer with additional tooling/scripts that set storage classes groups on collections. Storage classes groups could be used for moving data into long-term storage (e.g. Glacier, tape backup, etc). As an example, the user would change the storage class group to "glacier", which would copy the blocks into offline storage and delete them from the online storage. To retrieve the blocks, the user would change the storage class group to "s3". This would fetch the blocks and copy them back to online storage. (TBD: how does the client find out when the data actually becomes available.) h2. Development tasks # keepstore: configurable class list group per volume/mount # keepstore: support x-keep-storage-classes x-keep-storage-group header # apiserver: collections.desired_storage_classes column collections.desired_storage_group column, site default group (probably called "default") # keep-balance: compute/report desired and actual storage classes group(s) for each block