HP 3PAR RedHat and Oracle Linux Implementation Guide

NOTE: Even though the default discard option for creating filesystem is performed on ext2, ext3,
or ext4 filesystems, the mount option -o discard is supported only on the ext4 filesystem, so the
space reclaim operation is also supported only on the ext4 filesystem.
If you are recreating a file system on an existing TPVV, HP recommends that you use the default
discard option, as it will free up space on the HP 3PAR StoreServ Storage storage volume for data
that was not deleted before recreation.
Example:
# mkfs.ext4 /dev/mapper/350002ac000020121p1
Use the showvv -s <VV> command to get the space details on the storage volume. Here, the
Used column under Usr is the space used by the file system, Tot_Rsvd is the space allocated
on the storage volume, and VSize is the actual size that the file system can grow to, or total
volume size. Tot_Rsvd will be higher than the Used space because of additional space allocated
by the system to accommodate new writes and to avoid I/O delays due to volume growth.
In the following example, the host had 60 GB of data on an ext4 file system and files were
deleted, causing UNMAP to be issued. Consequently, the file system space is now 25 G and
allocated storage space is 60 G.
cli % showvv -s rhvol.3
---Adm--- ---------Snp---------- ----------Usr-----------
--(MB)--- --(MB)--- -(% VSize)-- ---(MB)---- -(% VSize)-- ------(MB)------
Id Name Prov Type Rsvd Used Rsvd Used Used Wrn Lim Rsvd Used Used Wrn Lim Tot_Rsvd VSize
96 rhvol.3 tpvv base 256 66 0 0 0.0 -- -- 60928 25172 1.6 0 0 61184 1536000
---------------------------------------------------------------------------------------------
1 total 256 66 0 0 60928 25172 61184 1536000
After space reclaim and defrag operations are run in the system, the Tot_Rsvd space is nearly
equal to the Used space.
root@inoded1062:S289_1# showvv -s rhvol.3
---Adm--- ---------Snp---------- ----------Usr-----------
--(MB)--- --(MB)--- -(% VSize)-- ---(MB)---- -(% VSize)-- ------(MB)------
Id Name Prov Type Rsvd Used Rsvd Used Used Wrn Lim Rsvd Used Used Wrn Lim Tot_Rsvd VSize
96 rhvol.3 tpvv base 384 148 0 0 0.0 -- -- 28928 25172 1.6 0 0 29312 1536000
---------------------------------------------------------------------------------------------
1 total 384 148 0 0 28928 25172 29312 1536000
The space-reclaim and defrag operations are automatically throttled and run at different time
intervals in the system, and space is reclaimed over a given interval of time rather than immediately
upon receiving the UNMAP command. The Used space will not be the same as is shown in the df
-k output because of file fragmentation and the way the inode table uses blocks on the system.
Symantec Space Reclaim Support
Symantec provides space reclaim support on TPVVs using the WRITE SAME SCSI primitive, which
is supported by HP 3PAR OS.
Use the vxdisk -o thin list to show that the type of disk is thinrclm. The thin reclaim is supported
using the vxdisk reclaim command. See Symantec documentation for details.
UNMAP Storage Hardware Primitive Support for RHEL 6.x 125