mount_acfs(8) mount_acfs(8)
NAME
mount_acfs - mount an Xsan volume
SYNOPSIS
mount_acfs [options] volume dir
DESCRIPTION
mount_acfs is a mount helper utility that mounts an Xsan volume on
client machines. This command is normally executed by mount(8) when
the -t acfs option is used.
Each client file system must communicate with a File System Manager
(FSM) running either locally or on a remote host. The FSM manages all
the activity for the client in terms of storage allocation and metada-
ta. Data transfers go directly between disks and the client.
OPTIONS
Options supported by the mount command:
-f LINUX ONLY
Fakes the mount process but updates the /etc/mtab file. The
mount call will fail if the mtab entry already exists.
-n LINUX ONLY
Mounts the filesystem without updating the /etc/mtab file.
-v Verbose mode.
Additional options may be specified in the /etc/fstab file or on the
mount(8) command line via the -o parameter. The -o parameter should be
specified only once. If multiple options are needed, they should fol-
low the -o in a comma-separated list.
ro Default: rw
Mount the file system read-only.
rw Default: rw
Mount the file system read/write.
compat32
Default: off
When set, force directory offsets to fit into 31 bits and inode
numbers to 32 bits. This should only be used when a problem has
been identified with using the full size of the struct dirent
d_off field from readdir(2) or older clients that are unable to
handle large inode numbers.
noexec Default: off
Do not allow the execution of programs resident on this file
system.
nosuid Default: off
When executing programs resident on this file system, do not
honor the set-user-ID and set-group-ID bits.
threads=n
Default: 12
Determines the number of kernel threads that are created.
threads will show up as cvfsiod processes in the output of ps.
Each client file system dedicates one thread to managing a sock-
et used to communicate with the FSM. The other threads handle
unsolicited messages.
This setting does not affect other kernel threads, for example,
cvfsd, cvfsbufiod, cvfsflusher, cvfs_dputter.
The minimum value allowed is 12.
stripeclusters=n
IGNORED ON OS X Default: 8
In certain cases, such as with using JBOD devices it may be pos-
sible to over-load their command queues using Xsan. If this oc-
curs, the I/O concurrency can be reduced by reducing the number
of concurrent stripeclusters the file system uses. The reduction
is at the cost of performance.
buffers={yes|no}
IGNORED ON OS X Default: yes
When set to yes, the file system will use buffer caching for un-
aligned I/O.
diskless={yes|no}
Default: no
If the diskless option is set to yes then the mount will suc-
ceed, even if the volume's disks are unavailable. Any subsequent
I/O will fail until the volume's disks are visible through the
Xsan portmapper.
diskproxy={server|client}
If the diskproxy option is set to client, then the mount will
use a Proxy Server to do its data I/O.
If the diskproxy option is set to server, then this system will
become a Proxy Server for this file system. A dpserver configu-
ration file must exist to define the operating parameters for
the Server. See dpserver(4) and sndpscfg(8) for details.
A set of proxy servers may be configured in a sparse manner
where each server sees only a subset of the disks in the file
system. The servers make use of the "diskless" mount option. The
proxy client will issue disk i/o requests to the appropriate
server. No special configuration is needed on the client.
Note: The diskproxy option is available only on Linux, OS X, and
Solaris systems, and the server option is available on Linux
systems. The diskproxy selection on Windows clients is made
through the Client Configuration utility.
proxypath={balance|rotate|sticky|filestickybalance|filestickyrotate}
Only used if the diskproxy option is set to client, controls the
algorithm used to balance I/O across Proxy Server connections.
The proxy client keeps track of bytes of I/O pending, bytes of
I/O completed and the elapsed time for each I/O request. It uses
these values and certain rules to determine the server that is
used for subsequent I/O requests. These collected counters are
decayed over time so that only the most recent (minute or so)
I/O requests are relevant.
There are two main components of the selection - the algorithm
itself and the use of file sticky behavior. The algorithms are
balance, rotate and sticky.
The balance algorithm attempts to keep the same amount of time's
worth of I/O outstanding on each connection. i.e. Faster links
will tend to get more of the I/O. A link could be faster be-
cause a given server is more efficient or less busy. It also may
be the case that network traffic over a given link uses higher
speed interconnects such as 10G ethernet.
The rotate algorithm attempts to keep the same number of bytes
of I/O pending on each Proxy Server connection. This is similar
to balance in that servers which respond more quickly to I/O re-
quests will have the outstanding I/O bytes reduced at a more
rapid pace than slower servers and will thus be used more often
than slower links.
The difference between balance and rotate is that with balance,
higher speed links will have more bytes of I/O outstanding than
slower links.
In both balance and rotate, if more than one path has the best
score, a pseudo-random selection among the winning paths is made
to break the tie.
The sticky algorithm assigns I/O to specific luns to specific
Proxy Server connections.
Filesticky behavior attempts to assign I/O for a given file to a
specific proxy server. It does this by using the file's inode
number modulo the number of servers to select a server index.
Since all clients see the same inode number for a given file,
all clients will select the same server. If there is more than
one path to that server, then the algorithm (balance or rotate)
will be used to select among the paths.
Filesticky behavior is controlled through a mount option.
When no proxypath mount option is specified, the balance algo-
rithm is used and filesticky behavior is selected.
For mount options balance and rotate, filesticky is not select-
ed. For filestickybalance and filestickyrotate filesticky is se-
lected.
Note: The proxypath mount option is available only on Linux, OS
X, and Solaris systems. The proxypath options are selected on
Windows clients through the Client Configuration utility.
proxyclient_rto=n
Only used if the diskproxy option is set to client. Defines the
starting value in seconds to wait for a Proxy Client I/O read
request to complete before disconnecting from the Proxy Server
and resubmitting the request to a different Proxy Server. If
reads are completing but coming close to the configured timeout,
the timeout will be increased.
The minimum value is 1 second, maximum is 3600 and the default
value is 15.
Note: This option is available only on Linux, OS X, and Solaris
systems.
proxyclient_wto=n
Only used if the diskproxy option is set to client. Defines the
starting value in seconds to wait for a Proxy Client I/O write
request to complete before disconnecting from the Proxy Server
and resubmitting the request to a different Proxy Server. If
writes are completing but coming close to the configured time-
out, the timeout will be increased.
The minimum value is 1 second, maximum is 3600 and the default
value is 30.
Note: This option is available only on Linux and Solaris sys-
tems.
atimedelay={yes|no}
Default: no
Perform lazy atime updates. This option improves performance by
waiting until closing a file before updating the atime value of
the file. This reduces extra network traffic and latency linked
to atime updates.
nrtiotokenhold=n
Default: 60
The QOS Token Hold Time (nrtiotokenhold) parameter is only ap-
plicable when using the Xsan Quality of Service (QOS) feature
for real-time I/O. The parameter determines the number of sec-
onds that a client storage pool will hold on to a non-realtime
I/O token during periods of inactivity. If no I/O is performed
on a storage pool within the specified number of seconds, the
token will be released back to the FSM.
The parameter should be specified in five second increments; if
the parameter is not a multiple of five, it will be rounded up
automatically.
auto_concwrite={yes|no}
Default: no
When set to yes, allows multiple threads to write to files con-
currently.
Note: setting auto_concwrite=yes requires that sparse=no also be
specified. Also, protect_alloc=yes is disallowed with auto_con-
cwrite=yes.
verbose={yes|no}
Default: no
When set to yes, mount_acfs will display configuration
information about the volume being mounted.
debug={yes|no}
Default: no
When set to yes, mount_acfs will display debugging infor-
mation. This can be useful in diagnosing configuration or
disk problems.
mnt_retrans=n
Default: 1
Indicates the number of retransmission attempts the file
system will make during the execution of the mount(2)
system call. Until the volume is mounted, the kernel will
only retransmit messages to the FSM mnt_retrans times.
This parameter works in conjunction with the mnt_recon
parameter. This can help reduce the amount of time a
mount command will hang during boot; see the mnt_type op-
tion.
mnt_recon={hard|soft}
Default: soft
Controls whether after mnt_retrans attempts at contacting
the FSS during the mounting and unmounting of a volume,
the kernel will either give up or continue retrying for-
ever. It is advisable to leave this option at soft so
that an unresponsive FSS does not hang the client during
boot.
mnt_type={bg|fg}
Default: fg (foreground)
Setting mnt_type to bg will cause the mount to run in the
background if the mount of the indicated volume fails.
mount_acfs will retry the mount mnt_retry number of times
before giving up. Without this option, an unresponsive
FSM could cause a machine to hang during boot while at-
tempting to mount Xsan volumes.
During background mounts, all output is re-directed to
/var/adm/SYSLOG.
mnt_retry=n
Default: 100
If a mount attempt fails, retry the connection up to n
times.
retrans=n
Default: 5
Indicates the number of attempts that the kernel will
make to transmit a message to the FSM. If no response to
a transmitted message arrives in the amount of time indi-
cated by the timeout parameter, the request will be re-
transmitted. If the volume was mounted with the re-
con=soft parameter, the file system will give up after
retrans attempts at sending the message to the FSM and
will return an error to the user.
recon={hard|soft}
Default: hard
This option controls whether after retrans attempts at
sending a message to the FSM, the file system will give
up or continue retrying forever. For hard mounted vol-
umes, the kernel will retry the connection attempt forev-
er, regardless of the value of the retrans field. For
soft mounted volumes, the kernel will only try retrans
number of times before giving up and returning an error
of ETIME (62).
timeout=n
Default: 100 (ten seconds)
The timeout value, in tenths of a second (0.1 seconds) to
use when sending message to the FSM. If no response is
received from the FSM in the indicated period the request
is tried again. On heavily loaded systems, you may want
to adjust the timeout value higher.
syslog={none|notice|info|debug}
Default: notice
During normal operations, certain messages will be logged
to the system console using the syslog facility. debug is
the most verbose, with notice being reserved for critical
information. It is important to note that the syslog
level is global per system, not unique to each volume.
Changing the level for one volume will affect all other
Xsan volumes.
blkbufsize=n
IGNORED ON OS X Default: 64 K
This option sets the maximum buffer size, in bytes, for
the unaligned I/O transition buffer. Use caution when
setting this option since values that are too small may
degrade performance or produce errors when performing
large unaligned I/O.
dircachesize=n
Default: 10 MB
This option sets the size of the directory cache. Direc-
tory entries are cached on the client to reduce client-
FSM communications during directory reads. Note: the di-
rectory cache on a client is shared across all mounted
Xsan volumes. If different values of dircachesize are
specified for multiple file systems, the maximum is used.
When applying this setting, ensure that the system has
sufficient kernel memory.
Can be specified in bytes (e.g. 2097152), kilobytes (e.g.
2048k), or megabytes (e.g. 2m).
auto_dma_read_length=n
IGNORED ON OS X Default: 1048577 Bytes (1MB + 1)
The minimum transfer size used for performing direct DMA
I/O instead of using the buffer cache for well-formed
reads.
The minimum value is the cachebufsize. By default, well-
formed reads of greater than 1 Megabyte will be trans-
ferred with DMA; smaller reads will use the buffer cache.
Auto_dma_read_length can be specified in bytes (e.g.
2097152), kilobytes (e.g. 2048k), or megabytes (e.g. 2m).
auto_dma_write_length=n
IGNORED ON OS X Default: 1048577 Bytes (1MB + 1)
The minimum transfer size used for performing direct DMA
I/O instead of using the buffer cache for well-formed
writes. All well-formed writes equal to, or larger than
this value will be transferred with DMA. All write trans-
fers of a smaller size use the buffer cache.
The minimum value is the cachebufsize. By default, well-
formed writes of greater than 1 Megabyte will be trans-
ferred with DMA; smaller writes will use the buffer
cache. Writes larger than this value, that are not well-
formed will use a temporary memory buffer, separate from
the buffer cache.
Auto_dma_write_length can be specified in bytes (e.g.
2097152), kilobytes (e.g. 2048k), or megabytes (e.g. 2m).
cvnode_max=n
Default: varies by platform.
This option sets the maximum number of cvnode entries
cached on the client. Caching cvnode entries improves
performance by reducing Client-FSM communication. Howev-
er, each cached cvnode entry must be maintained by the
FSM as well. In environments with many Xsan clients the
FSM may be overloaded with cvnode references. In this
case reducing the size of the client cvnode cache will
alleviate this issue.
max_dma=n
AIX AND LINUX ONLY
Default: varies by platform.
This option tells the kernel the maximum DMA size a user
process can issue. This can impact the number of concur-
rent I/Os the file system issues to the driver for a user
I/O. There are other factors that can also limit the num-
ber of concurrent I/Os. The default is 256m on AIX and
512m on Linux. WARNING: Incorrectly setting this value
may degrade performance or cause a crash/hang.
max_dev=n
AIX AND LINUX ONLY
Default: AIX: I/O driver IOCINFO max_transfer.
Default: Linux: 512M with Linux DM/Multipath. 512K with
StorNext multipath.
This option tells the kernel the maximum I/O size to use
when issuing I/Os to the underlying disk driver handling
a LUN. The file system attempts to get the maximum I/O
size using the IOCINFO ioctl. Since the ioctl is not al-
ways reliable, this mount option exists to override the
ioctl return value. Example usage max_dev=1m or
max_dev=256k. WARNING: Incorrectly setting this value
may result in I/O failures or cause a crash/hang. For
Linux clients, only use when recommended by Quantum Sup-
port.
sparse={yes|no}
Default: yes.
Some utilities detect "holes" in a file and assume the
file system will fill the hole with zeroes. To ensure
that Xsan writes zeroes to allocated, but uninitialized
areas on the disk, set sparse=yes.
DISK DEVICES
mount_acfs will query the local portmapper for the list of all
accessible Xsan disk devices. Xsan disks are recognized by their
label. This list is matched with the list of devices for each
storage pool in the volume. If any disk is missing, I/O will be
prohibited, and you will receive I/O errors.
RECONNECT
A socket is maintained for each unique Xsan client file system
for sending and receiving commands to and from the FSM. If the
socket connection is lost for any reason, it must be reconnect-
ed.
There are two daemons involved in re-establishing the connection
between an Xsan client and the FSM. The first is the socket in-
put daemon, which is a dedicated daemon that handles all input
from the FSM. The second is the reconnect daemon, which handles
the work of re-establishing the logical connection with the FSM.
Both of these daemons appear as cvfsd in the output from ps.
Messages will be printed on the system console and to syslog
during reconnect processing; the verbosity of the messages dis-
played can be controlled via the syslog= parameter and cvdb(8).
When the socket input daemon detects that the connection has
been lost, it will attempt to first connect to the fsm portmap-
per process, fsmpm(8). Once it has succeeded and has the port
number of the fsm(8)
to use, it attempts to create a new socket to the FSM using the
port number returned by fsmportmapper.
If no response is received from either the Xsan portmapper or
the FSM, the daemon will pend for the amount of time specified
by the timeout= parameter. The socket input daemon will attempt
to reconnect to the FSM forever.
If any of the configuration parameters in the FSM configuration
file changed, then the connection will be terminated, and no
further I/O will be allowed. The only recourse will be to un-
mount and remount the volumes. See snfs_config(5) (part of the
cvfs_server product) for more information on configuring the
FSM.
INTERRUPTIBLE SLEEPS
Whenever a process must go to sleep in the Xsan file system, the
sleep is interruptible, meaning that the process can be sent a
signal and the operation will fail with an error (usually EIN-
TR). The only exceptions are when a process is executing the ex-
it(2) system call and is closing out all open files; due to Unix
limitations, processes are immune to signals at that point.
EXAMPLES
To mount a volume that is described by the FSS configuration
file myvolume.cfg on that host:
mount -t acfs myvolume /usr/tmp/foo
SEE ALSO
cvfsd(8), cvdb(8), mount(8), chkconfig(8)
Xsan File System December 2015 mount_acfs(8)
Mac OS X 10.12.3 - Generated Thu Feb 9 18:55:30 CST 2017