Soft Partitioning for SVM

sunyeait

                非常经典的一篇关于soft partition for SVM的介绍。。。管方网页时不时访问不到，放在这儿以备急用
http://www2.primushost.com/~griff/soft-partitions.html
Solstice DiskSuite / Solaris Volume ManagerSoft PartitioningA Primer for Understanding Soft Partitioning,a new feature in Solstice DiskSuite (Solaris Volume Manager)The intent of this document is to describe Soft Partitioning within Solstice DiskSuite (soon-to-be-renamed Solaris Volume Manager), and offer a short primer/tutorial on how to create, use, and delete them.Until now, Solaris, without any volume management software, has only ever allowed a fixed number of partitions on a physical disk (seven (7) on SPARC platforms). With the increase in capacity of disks, this limitation has become a severe restriction.SDS/SVM uses these slices for its metadevices (sub-mirrors, trans, stripes, and RAID5) and hence is faced with the same limitation, whereas Veritas Volume Manager (VxVM) allows for the logical partitioning of disks into a virtually unlimited number of subdisks.Soft Partitioning allows for a disk to be subdivided into many partitions which are controlled and maintained by software, thereby removing the limitation of the number of partitions on a disk. A soft partition is made up of one or more "extents". An extent describes the parts of the physical disk that make up the soft partition. While the maximum number of extents per soft partition is 2147483647, the majority of soft partitions will use only one (1) extent.What is new?Soft Partitioning was not in the original Solstice DiskSuite 4.2.1 Release, which coincided with the release of Solaris 8. However, the soft partitioning functionality was released in patch 108693-06 for SDS 4.2.1.When Solaris 9 gets released, the "Solstice DiskSuite" name will change to "Solaris Volume Manager" ("SVM") and it will be bundled in with Solaris 9. Soft Partitioning will, of course, be part of the base functionality of that release.Soft Partitions are implemented by new kernel driver: md_sp.   # modinfo | grep md_sp   228 78328000 4743 - 1 md_sp (Meta disk soft partition module)There are new options to the metainit command:   metainit softpart -p [-e] component size   metainit softpart -p component -o offset -b sizeThe metattach command has been modified to allow for growing of soft partitions:   metattach softpart sizeThere is a new command... metarecover:   metarecover [-n] [-v] component -p [-d|-m]NOTE: the -p option means that the command refers to soft partitions.Creating Soft PartitionsThere are three methods to create a soft partition using the metainit command:   1. Specifying an unused disk and size (with the -e option). For example:         # metainit d0 -p -e c1t0d0 200m      The -e option requires that the name of the disk supplied be in the form c#t#d#.      The last parameter (200m) specifies the initial size of the soft partition. The sizes can be specified in blocks, kilobytes, megabytes, gigabytes, and terabytes.      The -e option causes the disk to be repartitioned such that slice 7 has enough space to hold a replica (although no replica is actually created on this disk) and slice 0 contains the rest of the space. Slice 2 is removed from the disk. The soft partition that is being created is put into slice 0. Further soft partitions can be created on slice 0 by the next method of creating a soft partition.      After this command is run, the layout of the disk would like similar to this example:         Part      Tag   Flag   Cylinders     Size           Blocks           0 unassigned   wm     5 - 2035   999.63MB   (2031/0/0) 2047248           1 unassigned   wm     0            0        (0/0/0)          0           2 unassigned   wm     0            0        (0/0/0)          0           3 unassigned   wm     0            0        (0/0/0)          0           4 unassigned   wm     0            0        (0/0/0)          0           5 unassigned   wm     0            0        (0/0/0)          0           6 unassigned   wm     0            0        (0/0/0)          0           7 unassigned   wu     0 -   4      2.46MB   (5/0/0)       5040      This command (with the -e) can only be run on an empty disk (one that is not used in any other metadevice). If another metadevice or replica already exists on this disk, one of the following messages will be printed, and no soft partition will be created.         metainit: hostname: c#t#d#s0: has appeared more than once in the specification of d#      or         metainit: hostname: c#t#d#s#: has a metadevice database replica   2. Specifying an existing slice name and size (without the -e option). This will be the most common method of creation. For example:          # metainit d1 -p c1t0d0s0 1g      This will create a soft partition on the specified slice. No repartitioning of the disk is done. Provided there is space on the slice, additional soft partitions could be created as required. The device name must include the slice number (c#t#d#s#).      If another soft partition already exists in this slice, this one will be created immediately after the existing one. Therefore, no overlap of soft partitions can occur by accident.   3. Specifying an existing slice and absolute offset and size values. For example:         # metainit d2 -p c1t0d0s0 -o 2048 -b 1024      The -o parameter signifies the offset into the slice, and the -b parameter is the size for the soft partition. All numbers are in blocks (a block is 512 bytes). The metainit command ensures that extents and soft partitions do not overlap. For example, the following is an attempt to create overlapping soft partitions.         # metainit d1 -p c1t0d0s0 -o 1 -b 2024         d1: Soft Partition is setup         # metainit d2 -p c1t0d0s0 -o 2000 -b 2024         metainit: hostname: d2: overlapping extents specified      An offset of 0 is not valid, as the first block on a slice containing a soft partition contains the initial extent header. Each extent header consumes 1 block of disk and each soft partition will have an extent header placed at the end of each extent. Extent headers are explained in more detail in the next section.      NOTE: This method is not documented in the man page for metainit and is not recommended for manual use. It is here because a subsequent metastat -p command will output information in this format. Extent HeadersWhenever a soft partiton is created in a disk slice, an "extent header" is written to disk. Internally to Sun, these are sometimes referred to as "watermarks".An extent header is a consistency record and contains such information as the metadevice (soft partition) name, it's status, it's size, and a checksum. Each extent header 1 block (512 bytes) in size.The following diagram shows an example 100MB slice (c1t0d0s0) and the extent headers (watermarks) that have been created on it. The command to make the soft partition shown was   # metainit d1 -p c1t0d0s0 20m->>There is always an extent header on the first and last blocks in the slice. Note that the 80MB of space left over from the creation of the soft partition can be used to make one or more additional soft partitions. Each additional soft partition will create an additional extent header to be created as well.Mirroring Soft PartitionsOnce you have created soft partitions, what can you do with them? Well, one thing to do is to create mirrors out of them. Unfortunately, even though a soft partition is a metadevice, they cannot serve directly as a submirror. For example:   # metainit d10 -p c1t11d0s4 100m   d10: Soft Partition is setup   # metainit d20 -m d10   metainit: hostname: d10: invalid unitInstead, you must first take the soft partition and create a simple concat/stripe out of it. For example:   # metainit d10 -p c1t0d0s0 100m   d10: Soft Partition is setup   # metainit d20 1 1 d10   d20: Concat/Stripe is setup   # metainit d30 -m d20   d30: Mirror is setup   # metainit d11 -p c2t0d0s0 100m   d11: Soft Partition is setup   # metainit d21 1 1 d11   d21: Concat/Stripe is setup   # metattach d30 d21   d30: submirror d21 is attachedOnce done, the resulting metastat output of the mirror will look like this:   # metastat d30   d30: Mirror       Submirror 0: d20         State: Okay       Submirror 1: d21         State: Okay       Pass: 1       Read option: roundrobin (default)       Write option: parallel (default)       Size: 204624 blocks   d20: Submirror of d30       State: Okay       Size: 204624 blocks       Stripe 0:           Device              Start Block  Dbase State        Hot Spare           d10                        0     No    Okay   d10: Soft Partition       Component: c1t0d0s0       State: Okay       Size: 204800 blocks           Extent              Start Block              Block count                0                        1                   204800   d21: Submirror of d30       State: Okay       Size: 204624 blocks       Stripe 0:           Device              Start Block  Dbase State        Hot Spare           d11                        0     No    Okay   d11: Soft Partition       Component: c2t0d0s0       State: Okay       Size: 204800 blocks           Extent              Start Block              Block count                0                        1                   204800Combining Soft Partitions Together into a RAID5 DeviceRAID5 devices can be made up of soft partitions directly. This example shows 4 soft partitions (from 4 separate slices) striped together to make a RAID5 device:   # metainit d1 -p c1t0d0s0 10m   d1: Soft Partition is setup   # metainit d2 -p c2t0d0s0 10m   d2: Soft Partition is setup   # metainit d3 -p c3t0d0s0 10m   d3: Soft Partition is setup   # metainit d4 -p c4t0d0s0 10m   d4: Soft Partition is setup   # metainit d10 -r d1 d2 d3 d4   d10: RAID is setupOnce done, the resulting metastat output of the RAID5 device will look like this:   # metastat d10   d10: RAID       State: Okay       Interlace: 32 blocks       Size: 59472 blocks   Original device:       Size: 60384 blocks           Device              Start Block  Dbase State        Hot Spare           d1                       330     No    Okay           d2                       330     No    Okay           d3                       330     No    Okay           d4                       330     No    Okay   d1: Soft Partition       Component: c1t0d2s0       State: Okay       Size: 20480 blocks           Extent              Start Block              Block count                0                        1                    20480   d2: Soft Partition       Component: c1t0d4s0       State: Okay       Size: 20480 blocks           Extent              Start Block              Block count                0                        1                    20480   d3: Soft Partition       Component: c1t1d1s0       State: Okay       Size: 20480 blocks           Extent              Start Block              Block count                0                        1                    20480   d4: Soft Partition       Component: c1t1d3s0       State: Okay       Size: 20480 blocks           Extent              Start Block              Block count                0                        1                    20480Using Soft Partitions for MetaTrans (UFS Logging) DevicesMetaTrans devices (UFS logging) can be built on top of soft partitions. Soft partitions can be used for the master device, the logging device, or both. In the following example, soft partitions are used for both the master and the logging device:   # metainit d1 -p c1t0d0s0 500m   d1: Soft Partition is setup   # metainit d2 -p c2t0d0s0 50m   d2: Soft Partition is setup   # metainit d10 -t d1 d2   d1: Trans is setupOnce done, the resulting metastat output of the metatrans device will look like this:   # metastat d10   d10: Trans       State: Okay       Size: 1024000 blocks       Master Device: d1       Logging Device: d2   d1: Soft Partition       Component: c1t1d3s0       State: Okay       Size: 1024000 blocks           Extent              Start Block              Block count                0                        1                  1024000   d2: Logging device for d10       State: Okay       Size: 102142 blocks   d2: Soft Partition       Component: c1t1d1s0       State: Okay       Size: 102400 blocks           Extent              Start Block              Block count                0                        1                   102400LayeringMost of the time, soft partitions are made on a disk slice. However, there are certain situations where it can be beneficial to make a soft partition on top of an existing metadevice. This is referred to as layering.For example, say you have a 90GB RAID5 device made up of 6 18GB disks. You can then take that 90GB device and "split it up" into many soft partitions. These many soft partitions then can be accessed as separate simple metadevices, although the data in them is protected by the RAID5 parity in the underlying device.Soft partitions can be layered only on top of concat/stripes, mirrors, and RAID5 devices. Soft partitions cannot be layered on top of a metatrans device or directly on top of another soft partition.Here is an example of layering soft partitions on top of an existing RAID5 metadevice. First, we create the RAID5 device, then soft partition that device into 3 100MB partitions (obviously, we could create more than just 3 soft partitions).   # metainit d0 -r c1t0d2s0 c1t0d4s0 c1t1d1s0 c1t1d3s0   d0: RAID is setup   # metainit d1 -p d0 100m   d1: Soft Partition is setup   # metainit d2 -p d0 100m   d2: Soft Partition is setup   # metainit d3 -p d0 100m   d3: Soft Partition is setupEach of the resulting soft partitions (d1, d2, and d3) can be accessed individually (i.e., newfs and mount).Soft partitions can be built on top of an existing mirror device as well, just like we did above on the RAID5 device. In the following example, the mirror device (d0) is "carved up" into 3 smaller soft partitions.   # metainit d10 1 1 c1t0d2s0   d10: Concat/Stripe is setup   # metainit d20 1 1 c2t0d0s0   d20: Concat/Stripe is setup   # metainit d0 -m d10 d20   d0: Mirror is setup   # metainit d1 -p d0 100m   d1: Soft Partition is setup   # metainit d2 -p d0 100m   d2: Soft Partition is setup   # metainit d3 -p d0 100m   d3: Soft Partition is setupSoft partitions are not allowed to be parented by other soft partitions directly. For example:   # metainit d1 -p c1t0d0s0 100m   d1: Soft Partition is setup   # metainit d2 -p d1 10m   metainit: hostname: d1: invalid unitSoft partitions also cannot be built on top of trans (UFS logging) devices. For example:   # metainit d1 -t d10 d20   d1: Trans is setup   # metainit d2 -p d1 100m   metainit: hostname: d1: invalid unitGrowing Soft PartitionsA soft partition can be grown by the use of the metattach command. There is no mechanism to shrink a soft partition.   # metattach d0 10m   d0: Soft Partition has been grownWhen additional space is added to an existing soft partition, the additional space is taken from any available space on the same device and might not be contiguous with the existing soft partition. Growing soft partitions must be done with free space in the same device as the current soft partition.The following example shows how growing a soft partition will increase the size of the current extent:   # metainit d1 -p c1t0d2s0 100m   d1: Soft Partition is setup   # metastat d1   d1: Soft Partition       Component: c1t0d2s0       State: Okay       Size: 204800 blocks           Extent              Start Block              Block count                0                        1                   204800   # metattach d1 50m   d1: Soft Partition has been grown   # metastat d1   d1: Soft Partition       Component: c1t0d2s0       State: Okay       Size: 307200 blocks           Extent              Start Block              Block count                0                        1                   307200Note how after the metattach is run, there is still only one extent, but the (block count) has grown from 204800 (100MB) to 307200 (150MB).In the following example, the extent cannot be grown, as it was above, because another soft partition is "in the way". Therefore, a second extent is created in the same slice.   # metainit d1 -p c1t0d2s0 100m   d1: Soft Partition is setup   # metainit d2 -p c1t0d2s0 10m   d2: Soft Partition is setup   # metastat   d1: Soft Partition       Component: c1t0d2s0       State: Okay       Size: 204800 blocks           Extent              Start Block              Block count                0                        1                   204800   d2: Soft Partition       Component: c1t0d2s0       State: Okay       Size: 20480 blocks           Extent              Start Block              Block count                0                   204802                    20480   # metattach d1 50m   d1: Soft Partition has been grown   # metastat   d1: Soft Partition       Component: c1t0d2s0       State: Okay       Size: 307200 blocks           Extent              Start Block              Block count                0                        1                   204800                1                   225283                   102400   d2: Soft Partition       Component: c1t0d2s0       State: Okay       Size: 20480 blocks           Extent              Start Block              Block count                0                   204802                    20480Note how d1 now has two non-contiguous extents that together make up the 307200 (150MB) blocks.NOTE: Growing the metadevice does not modify the data or the filesystem inside the metadevice. If the metadevice contains a filesystem, you must use the appropriate command(s) to grow that filesystem after the metadevice has been grown.Deleting Soft PartitionsThis is achieved by using the metaclear command in the normal way:   # metaclear d0   d0: Soft Partition is clearedIf other metadevices are using the soft partition, the metaclear will error with:   metaclear: hostname: d0: metadevice in useUsing Soft Partitions with DisksetsThere are no differences with soft partitioning in a diskset, other than having to specify the -s option on the commandline to specify the diskset name.The only potential problem occurs when dealing with did disk devices that are in a SunCluster configuration. Unfortunately, the naming convention of the did devices is similar to that of SDS/SVM in that the disks are referred to as d#. This means that SDS/SVM could confuse a did disk with a metadevice when creating a soft partition.The simple workaround to this problem is to use the full path to the did device on the metainint commandline in order to prevent any confusion.For example, the following command to create a 1GB soft partition on /dev/did/rdsk/d7s0 would be invalid:   # metainit -s set2 d0 -p d7s0 1gInstead, the correct command to run would be:   # metainit -s set2 d0 -p /dev/did/rdsk/d7s0 1gHow to list the soft partitions in a given sliceThe metarecover command, with the -n and -v options, will display information about the soft partitons existing in a given slice.The metarecover command actually scans the given slice for extent headers and prints the information that it finds about those headers.In each slice/device, there are also 2 additional extent headers; one which preceeds the free space in the slice, and the one on the last block of the slice. These are printed as well. This is an easy way to determine how much free space is available in a slice for additional soft partitions.   # metarecover -v -n /dev/rdsk/c1t0d0s0 -p   Verifying on-disk structures on c1t0d0s0.   The following extent headers were found on c1t0d0s0.    Name  Seq#    Type          Offset          Length      d0     0   ALLOC               0           20481      d1     0   ALLOC           20481           40961    NONE     0     END        17674901               1    NONE     0    FREE           61442        17613459   Found 2 soft partition(s) on c1t0d0s0.In the above example, there were 2 soft partitions (d0 and d1) found on c1t0d0s0, as well as 17613458 blocks (approx 8.4GB) of unallocated free space.IMPORTANT NOTE: The information printed by this command is relative to the extent header, not the soft partition itself. Therefore, the 'offset' is the starting location of the extent header, not the extent itself. Also, the 'length' given is the length of the extent plus the header. Therefore, in the example above, there are only 17613458 free blocks, not 17613459 blocks.Because soft partitions can be layered above metadevices like mirrors or RAID5 devices (see layering, above), this command can also be run on them to determine the locations and sizes of the extent headers. In the example below, d0 is a RAID5 metadevice which has 4 soft partitions in it. There is no free space left in this device.   # metarecover -v -n d0 -p   Verifying on-disk structures on d0.   The following extent headers were found on d0.                   Name  Seq#    Type               Offset               Length                     d1     0   ALLOC                    0               204801                     d2     0   ALLOC               204801               204801                     d3     0   ALLOC               409602               204801                    d99     0   ALLOC               614403              7573580                   NONE     0     END              8187983                    1   Found 4 soft partition(s) on d0.FragmentationFragmentation of free space will occur on a slice when there has been activity in creating, deleting, and possibly growing soft partitions. At this time, there is no method to defragment a disk.For example, the following sequence of commands can result in some amount of fragmentation. First, create 2 10MB soft partitions on a slice.   # metainit d1 -p c1t0d0s0 10m   d1: Soft Partition is setup   # metainit d2 -p c1t0d0s0 10m   d2: Soft Partition is setupThen, remove the first 10MB soft partition and then create a 20MB soft partition.   # metaclear d1   d1: Soft Partition is cleared   # metainit d3 -p c1t0d0s0 20m   d3: Soft Partition is setupWhen the d3 metadevice was created, the 10MB of free space at the beginning of the slice is not used, because there is a contiguous 20MB space available further out that can be used instead. Therefore, the 10MB of free space is skipped over in favor of the first 20MB of contiguous space. The metarecover command will show the fragmentation (multiple free spaces):   # metarecover -v -n c1t0d0s0 -p   Verifying on-disk structures on c1t0d0s0.   The following extent headers were found on c1t0d0s0.                Name  Seq#    Type               Offset               Length                  d2     0   ALLOC                20481                20481                  d3     0   ALLOC                40962                40961                NONE     0     END              2047247                    1                NONE     0    FREE                81923              1965324                NONE     0    FREE                    0                20481   Found 2 soft partition(s) on c1t0d0s0.Recovering Soft PartitionsThe 'metarecover' command is run when something has gone wrong. It should not be run except to recover from a catastrophic problem. There are two main functions that this command does. It can   1. scan through the given slice and recreate the soft partitions that it finds there. this is good when moving a disk with soft partitions to a new machine. The option to use on the metarecover command is -d.   2. reads through the current replica and creates the soft partitions on the given slice. This is good to run after a disk fails and gets replaced with a new one. The option to use on the metarecover command is -m. Recreating Information in the Replica from the Extent HeadersHere is a very simple example showing a disk which had soft partitions created on it (in slice 0) on another host, which is being moved to a new machine. We wish to extract the soft partitions on this new machine. Currently, there are no metadevices created.   # metastatThis command scans the given slice (in this case, "c0t0d0s0") and, for each soft partition it finds in that slice, it puts an entry into the current replica. The data on the disk is not modified, and nothing on the slice specified is modified. All that happens is that the extent headers are read and information is written to the replica.   # metarecover c0t0d0s0 -p -d   The following soft partitions were found and will be added to   your metadevice configuration.    Name            Size     No. of Extents     d1           61440         1     d2           20480         1   WARNING: You are about to add one or more soft partition   metadevices to your metadevice configuration.  If there   appears to be an error in the soft partition(s) displayed   above, do NOT proceed with this recovery operation.   Are you sure you want to do this (yes/no)? yes   c0t0d0s0: Soft Partitions recovered from device.Now, we can see the soft partition metadevices have been created for us:   # metastat   d1: Soft Partition       Component: c0t0d0s0       State: Okay       Size: 61440 blocks           Extent              Start Block              Block count                0                   120836                    61440   d2: Soft Partition       Component: c0t0d0s0       State: Okay       Size: 20480 blocks           Extent              Start Block              Block count                0                    20482                    20480Recreating Soft Partitions from Information in the ReplicaThis example essentially does the opposite of example 1. In this case, the actual extent headers on the disk have been lost, either because something wrote over them, or because the disk hosting the soft partitions had to be replaced with new disk drive. Although the replica shows the soft partitions to be "Okay":   # metastat   d1: Soft Partition       Component: c0t0d0s0       State: Okay       Size: 61440 blocks           Extent              Start Block              Block count                0                   120836                    61440   d2: Soft Partition       Component: c0t0d0s0       State: Okay       Size: 20480 blocks           Extent              Start Block              Block count                0                    20482                    20480there are no extent headers on the disk, so I/O to the disk will error out.   # dd if=/dev/zero of=/dev/md/rdsk/d2   dd: /dev/md/rdsk/d2: open: I/O errorTo check the disk to see if any extent headers exist on the disk, you can run the command   # metarecover -n c0t0d0s0 -p   found incorrect magic number 0, expected 20000127.   No extent headers found on c0t0d0s0.   c0t0d0s0: On-disk structures invalid or no soft partitions found.   metarecover: hostname: d0: bad magic number in extent headerThe above command confirms that there are no extent headers on the disk. To have the extent headers written out to the disk, according to the information currently in the replica, run the command   # metarecover c0t0d0s0 -p -m   c0t0d0s0: Soft Partition metadb configuration is valid   WARNING: You are about to overwrite portions of c0t0d0s0   with soft partition metadata. The extent headers will be   written to match the existing metadb configuration.  If   the device was not previously setup with this   configuration, data loss may result.   Are you sure you want to do this (yes/no)? yes   c0t0d0s0: Soft Partitions recovered from metadbNow, the extent headers have been written to the disk, so I/O will work correctly now. Running the verify command again, we see   # metarecover -n c0t0d0s0 -p   c0t0d0s0: Soft Partition metadb configuration is valid   c0t0d0s0: Soft Partition metadb matches extent header configuration
               
               
               
               
               

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