LU-930 doc: update lfs migrate usage and man page

[fs/lustre-release.git] / lustre / doc / lfs-migrate.1

diff --git a/lustre/doc/lfs-migrate.1 b/lustre/doc/lfs-migrate.1
index 7a8609d..795b5d3 100644 (file)
--- a/lustre/doc/lfs-migrate.1
+++ b/lustre/doc/lfs-migrate.1
@@ -1,67 +1,214 @@
-.TH LFS-MIGRATE 1 2015-12-07 "Lustre" "Lustre Utilities"
+.TH LFS-MIGRATE 1 2021-11-08 "Lustre" "Lustre Utilities"

 .SH NAME
 lfs migrate \- migrate files or directories between MDTs or OSTs.
 .SH SYNOPSIS
 .B lfs migrate
 .SH NAME
 lfs migrate \- migrate files or directories between MDTs or OSTs.
 .SH SYNOPSIS
 .B lfs migrate

-\fI-m mdt_idx\fR [-v|--verbose] \fI<directory>\fR
+.RB [ -h "] [" -v ]
+.RI [ SETSTRIPE_OPTIONS " ... ]"
+.IR FILE " ..."

 .br
 .br

-.B lfs migrate
-.RI [OPTIONS] ... <file|directory>\fR...
+.B lfs migrate -m \fISTART_MDT_INDEX
+.RB [ -cHv ]
+.I DIRECTORY

 .br
 .SH DESCRIPTION
 .br
 .SH DESCRIPTION

-Migrate MDT inodes or OST objects between MDTs and OSTs respectively. For the
-case of MDT inode migration:
+Migrate OST objects between OSTs for the specified
+.IR FILE ,
+or recursively migrate
+.I DIRECTORY
+and all inodes/directories therein between MDTs.
+.SH OST MIGRATE OPTIONS
+.P
+The
+.B lfs migrate
+command can be used for moving files from one (or more) OSTs to other
+OSTs (e.g. for space balancing between OSTs, or to evacuate an OST for
+hardware reasons), to change the stripe count or other layout parameters
+of a file (e.g. to increase the bandwidth of a file by striping it over
+multiple OSTs), or to move the file between different classes of storage
+(e.g. SSD vs. HDD OSTs, or local vs. remote OSTs in different pools).
+.P
+In OST object migration mode, the command supports the same
+.I SETSTRIPE_OPTIONS
+listed in
+.BR lfs-setstripe (1)
+to specify the layout of the target file.  The migrate command differs from
+.B lfs setstripe
+in that
+.B lfs migrate
+will copy the data from the existing file(s) using the new layout parameters
+to the new OST(s). In contrast,
+.B lfs setstripe
+is used for creating new (empty) files with the specified layout.
+For OST object migration, there additional options available:

 .TP
 .TP

-.B migrate -m|--mdt-index <mdt_idx> \fIdirectory\fR
-.br
-Move the file metadata (inode) from one MDT to MDT with index \fBmdt_idx\fR.
-Migration of striped directories or individual files between MDTs is not
-currently supported. Only the root user can migrate directories.  Files that
-have been archived by HSM or are currently open are skipped by MDT inode
-migration. Access to files within the directory is blocked until migration is
-complete.
-.TP
-\fIWARNING\fR
-A migrated file or directory will have a new inode number and FID.  As
-a consequence, files archieved by Lustre HSM cannot currently be migrated
-and migrated files that have a new inode number may confuse backup tools.
-.TP
-For the case of OST object migration:
-.TP
-.B migrate
-.B [--stripe-count|-c \fIstripe_count\fR]
-.B [--stripe-index|-i \fIstart_ost_idx\fR]
-.B [--stripe-size|-S \fIstripe_size\fR]
-.B [--pool|-p \fIpool_name\fR]
-.B [--ost-list|-o \fIost_indices\fR]
-.B [--block|-b]
-.B [--non-block|-n] \fIfile|directory\fR
-.B [--component-end|-E \fIcomp_end\fR]
-.br
-Migrate can also be used for OST objects by omitting \fI-m\fR option. In this
-mode, the command has identical options to
-.BR lfs-setstripe (1).
-The difference between migrate and setstripe is that \fImigrate\fR will
-re-layout the data in existing files using the new layout parameter by copying
-the data from the existing OST(s) to the new OST(s). In contrast,
-\fIsetstripe\fR is used for creating new files with the specified layout.  For
-more information, see lfs-setstripe(1).
+.BR -b , --block
+Block access to the file by other applications during data migration
+(default).  This prevents other processes from accessing the file during
+migration, which prevents data data writes to the old file objects from
+being lost.  This should be used if an OST needs to be completely emptied
+prior to its removal, to ensure all requested files are migrated off the
+OST.
+.TP
+.BR -h , --help
+Print usage message.
+.TP
+.BR -n , --non-block
+Abort migration if concurrent file access is detected.  This can be
+used with OST space balancing migration to avoid interfering with file
+access by applications if there is not a requirement to migrate any
+particular file to the new layout.
+.TP
+.BR -D , --non-direct
+Do
+.B not
+use
+.B O_DIRECT
+read and write operations when migrating a file.  The
+.B O_DIRECT
+option avoids data copy from kernel buffers into userspace, which can
+impose CPU and memory overhead on the copy operation, but makes read and
+write operations synchronous.  Using the
+.B --non-direct
+option uses buffered read/write operations, which may improve migration
+speed at the cost of more CPU and memory overhead.
+.TP
+.BR -v , --verbose
+Print each filename as it is migrated.

 .P
 .P

-NOTE: lfs migrate has a complementary script
+NOTE:
+.B lfs migrate
+has a complementary

 .B lfs_migrate
 .B lfs_migrate

-which is used to provide extra functionality when migrating file data
-between OSTs and has a separate man page.
-.SH EXAMPLES
+script which is used to provide extra functionality when migrating file
+data between OSTs and has a separate man page.  See
+.BR lfs_migrate (1)
+for details.
+.SH MDT MIGRATE OPTIONS
+.TP
+.BR -m , --mdt-index=\fIMDT_INDEX [, \fIMDT_INDEX ,...]
+The specified
+.I DIRECTORY
+.B and all subdirectories and inodes
+will be migrated to the MDT with the specified
+.IR MDT_INDEX .
+This is useful if new MDTs have been added to a filesystem and existing user or
+project directories should be migrated off old MDTs to balance the space usage
+and future metadata workload. If
+.I MDT_INDEX
+is -1, the MDT index will be balanced by free space and inodes among
+available MDTs.  If multiple
+.I MDT_INDEX
+values are specified in a comma-seperated list, then all
+subdirectories will be
+.B striped
+across all of the specified MDT indices as if an equivalent
+.BI -c N
+option were given.
+.TP
+.BR -c , --mdt-count=\fICOUNT\fR
+All directories and subdirectories in the tree will be striped across
+.I COUNT
+MDTs, always using
+.I MDT_INDEX
+as the primary MDT for the directory.  If
+.I MDT_INDEX is
+.B -1
+then
+.I COUNT
+directory stripes will be chosen from MDTs proportional to the amount
+of free inodes and space on each MDT.  If multiple
+.I MDT_INDEX
+values are specified in a comma-separated list, then the number of specified
+.I MDT_INDEX
+values must match
+.IR COUNT .
+.TP
+.BR -H , --mdt-hash=\fIHASH_TYPE\fR
+Use
+.I HASH_TYPE
+for the new directory layout.
+.RS 1.2i

 .TP
 .TP

-.B $ lfs migrate -m 0 ./testremote
-Move the inodes contained in ./testremote from their current MDT to the
-MDT with index 0.
+.B all_char (type 1)
+Sum of ASCII characters modulo number of MDTs. This
+provides weak hashing of the filename, and is suitable
+for only testing or when the input is known to have
+perfectly uniform distribution (e.g. sequential numbers).
+.TP
+.B fnv_1a_64 (type 2)
+Fowler-Noll-Vo (FNV-1a) hash algorithm.  This provides
+reasonably uniform, but not cryptographically strong,
+hashing of the filename. (default)
+.TP
+.B crush (type 3)
+CRUSH hash algorithm.  This is a consistent hash
+algorithm, so minimum sub files need to relocate
+during directory restripe.
+.RE
+.P
+.TP
+.B NOTE
+Only the root user can migrate directories.  Files that have been archived by
+HSM or are currently opened will fail to migrate, user can run the same migrate
+command again to finish migration when files are ready.  Both inode and
+directory entry will be migrated.  During migration directory and sub files can
+be accessed like normal ones, but the migration itself cannot be interrupted.
+.TP
+.B NOTE
+It is not currently possible to migrate files with an
+.B mdt
+component (Data-on-MDT, DoM).  If it is necessary to migrate such files off
+a particular MDT, they must first be migrated to have a non-DoM file layout
+and then the inodes migrated separately.  See
+.B EXAMPLES
+for details on how to migrate DoM files between MDTs.
+.TP
+.B WARNING
+Each migrated file or directory will have a new FID, and hence a new inode
+number.  As a consequence, files archived by Lustre HSM that depend on
+the FID as the identifier in the HSM archive cannot currently be migrated.
+Having a new inode number may also cause backup tools to consider the
+migrated file(s) to be a new, and cause them to be backed up again.
+.P
+.SH EXAMPLES

 .TP
 .B $ lfs migrate -c 2 /mnt/lustre/file1
 .TP
 .B $ lfs migrate -c 2 /mnt/lustre/file1

-This migrate the file into a new layout with 2 stripes.
+This migrates the data in
+.B file1
+into a new layout with 2 stripes.

 .TP
 .TP

-.B $ lfs migrate -E 64M -c 1 -E 256M -c 4 -E -1 -c -1 /mnt/lustre/file1
-This migrate the file into a three components composite layout.
+.B $ lfs migrate -E 256M -c 1 -E 16G -c 4 -E eof -c 40 /mnt/lustre/file2
+.br
+This migrates the data in
+.B file2
+into a three component composite layout (number of stripes depends on
+file size).
+.TP
+.B # lfs migrate -m 0,2 testremote
+.br
+Recursively move the subdirectories and inodes contained in directory
+.B remotedir
+from its current MDT to MDT0000 and MDT0002.  The
+.B testremote
+directory and all of its subdirectories will be striped across both MDTs.
+.TP
+.B # lfs setstripe -E 256M -c 1 -E 16G -c 4 -E eof -c 40 topdir
+Set a default PFL layout (without any DoM component) on the directory
+.BR topdir ,
+.TP
+.B # lfs find dir -type f -L mdt -0 | xargs -0 lfs migrate --copy topdir
+then find and migrate all regular files that have an
+.B mdt
+component to copy the default layout from the specified
+.BR topdir ,
+.TP
+.B # lfs migrate -m 2 topdir
+.br
+and finally migrate the directory
+.B topdir
+and all files and subdirectories in that tree to MDT0002.  This allows
+migrating files with DoM components off an MDT.

 .SH AUTHOR
 The lfs command is part of the Lustre filesystem.
 .SH SEE ALSO
 .SH AUTHOR
 The lfs command is part of the Lustre filesystem.
 .SH SEE ALSO