Storage Management: MirrorDisk/UX, Online JFS

•Introduction

•LVM Striping

•Mirror Disk / UX – Basics

•Online Backups (lvsplit)

•Mirror Disk / UX – Advanced

•Mirrored Boot Devices

•Snapshots

Introducing the Journal File System

Base Version Bundled

•Veritas Extended File System (VXFS)

•Fast fsck

•Extent-based allocation

•Enhanced mount options

On-line JFS Additional Features

•On-Line Defragmentation

•On-Line Backup – Snapshot

•On-Line Growth/Reduction

Software Disk Striping

•When you use disk striping you create a Logical Volume that spans multiple disks, allowing successive blocks of logical extents to map to different disks.

•Valid stripe sizes are 4k, 8k. 16k, 32k, and 64k. The default size is 16k. You should match the stripe size with the block size of the file system (or a number evenly divisible by the stripe size).

•EG: If the planned block size for a filesystem is 16k, the stripe size should be 4, 8, or 16k.

•Note: You cannot use striping and mirroring on the same logical volume.

Striping – Benefits and Costs

Benefits

•Data access performed over multiple disks simultaneously

•I/O can be balanced across interfaces

Costs

•Hardware failure on a single disk may result in loss of portions of many files

•Entire files must be restored, even though only a portion was lost

•Added complexity

•Maximizing the Benefits of Striping

Maximizing the Benefits of Striping

•To maximize the benefits of striping it is best to spread the volumes across separate interfaces.

•Best performance results from a striped logical volume that spans similar disks

•Select the appropriate stripe size

•For HFS file systems match the block size.

•For JFS file systems, always use 64K stripes.

•For RAW data choose a size that matches the primary I/O size for the application.

•Creating Striped Logical Volumes

Creating Striped Logical Volumes

lvcreate –i stripes –I stripe_size [-l | -L space] [-n name] VG

•-i number of disks to stripe across

•-I stripe size in kilobytes (4, 8, 16, 32, or 64)

•-l total space expressed in extents

•-L total space expressed in megabytes

•-n name of the logical volume

•EG: lvcreate –i 3 –I 8 –L 24 –n lvstripe /dev/vg01

Implementing Mirroring

LogicalLE: 0

LE: 1

LE: 56

LE: 107

/home/fred/file1

filesystem

LVM

Physical

PV0PE:0

PV1PE:0

Mirrored I/O Scheduling

Access PV with lowest outstanding I/Os

Read in PV order

Schedule writes inPV order.

Shedule writessimultaneously to all PVs

Parallel Sequential

READ

WRITE

I/O

LE 47

PE 93, PV0 PE 107, PV2 PE 606, PV1

Protecting from Disk FailurePV0 PV1 PV2

Mirrored I/O

•PV0 Scheduled - returned

•PV1 Scheduled - returned

•PV2 Scheduled, returned – retry – unavailable

•High priority write of PV status to VGRA on all available pvs.

Mirrored Write Cache

•Tracking of pending I/O is done in a cache called Mirrored Write Cache (MWC). The MWC holds the status of write I/Os to a relatively large areas of a logical volume called Logical Track Groups (LTG). When a write I/O is scheduled it is resolved onto the LTG it affects. This entry in the cache is marked dirty.

•The I/O is scheduled, and when it completes the I/O is marked clean.

•The MWC can be turned off

•Provides a runtime performance gain

•Mirror resync takes longer

•At volume group activation if MWC is off then /usr/sbin/nomwcsyncd is started to do a background mirror resync

•You can never run this manually, if necessary deactivate and reactivate the volume group.

LVM Commands for Mirroring

lvcreate [–m copies] [-L size in MB] VG

lvextend [-m copies] LV PV

lvreduce [-m copies] LV PV

lvdisplay –v LV

•You may have 0, 1, or 2 copies of any given logical volume

LVM Commands for Synchronization

lvsync LV

vgsync VG

•Resynchronizes from one copy to make all mirror copies consistent

•Automatically done when a volume group that is not currently active, is activated.

•Rarely done manually.

Online Backups

•In this example you see lvol2 is mirrored with one copy on PV0 and one on PV1.

•A lvsplit operation will freeze the mirror copy and create a ‘backup’ logical volume which points to it.

•This can now be mounted and used while activity continues on the other PV.

•If you have three mirrors when you do this, you can take the backup while continuing to have data protection for the active volume.

•Once a backup has completed you can use the lvmerge command to resynchronize the mirrors.

PV0

PV1

lvol2

lvol2b PV1

PV0lvol2

Base JFS / Online JFS

Base JFS Online JFS

Online Backup not possible online, snapshot

Extending fs offline, extendfs online, fsadm

Reducing fs not possible online, fsadm

Defragmenting fs not possible online, fsadm

Fast recovery fsck yes yes

fsadm

fsadm –F vxfs [-d] [-D] [-e] [-E] /mountpoint_dir

•fsadm-options:

-F vxfs specifies the journaled filesystem

-d Performs a directory defragmentation

-D Report on directory fragmentation

-e Performs a file extent defragmentation

-E Report on file extent fragmentation

•Regains lost performance

•Should be periodically used (between once a day and once a month)

•Can be done manually or scheduled with a cron-job

•The optimization runs online on a mounted JFS file system

Resizing

IncreaseLogicalVolume

IncreaseFilesystem

ReduceFilesystem

ReduceLogicalVolume

Increasing an Online JFS filesystem

•Extend the logical volume to the needed size:

# lvextend –L new_size lvol_name

The value of new_size is given in megabytes!

•Extend the JFS filesystem online:

# fsadm –F vxfs –b new_size /mountpoint

The value of new_size is given in kilobytes!

•Check the size of the increased file system:

# bdf

Reducing an Online JFS filesystem

•Reorganize directories/file extents:

# fsadm –F vxfs –d –D –e –E /mountpoint

•Reduce the JFS file system online:

# fsadm –F vxfs –b new_size /mountpoint

The value of new_size is given in kilobytes!

•Reduce the logical volume to the needed size:

# lvreduce –L new_size lvolname

The value of new_size is given in megabytes!

•Verify the size of the reduced file system:

# bdf

Online Backup via Snapshot

Original File system Snapshot File system

Process writes data

Buffer Cache

1

2

Original BlockNew Block

Copy of originalblock

3

/mountpoint

/snapshot_mnt

Creating a snapshot

•Create a snapshot

# mount –F vxfs –o snapof=/orig_vol /aux_vol /aux_dir

/orig_vol file system, which you want to take a snapshot of/aux_vol logical volume to hold the snapshot (no file system)/aux_dir directory to mount the snapshot

•Backup from the snapshot file system

# cd /aux_dir

# tar cvf /dev/rmt/0m or

# find . | cpio –ovcx > /dev/rmt/0m or

# vxdump –f /dev/rmt/0m /aux_dir

•Unmount the snapshot, then lvremove the volume