Fujitsu, the leading Japanese information and communication technology company, is the world’s fourth-largest IT services provider and offers a full range of technology products, solutions and services. Approximately 170,000 Fujitsu employees support customers in over 100 countries.
In October 2013, Fujitsu recommended PerfectStorage in a Customer Information Bulletin sent to its ETERNUS storage client base entitled “Space Reclamation in Windows Servers without UNMAP Support.” The bulletin was targeted to clients running Fujitsu ETERNUS DX S2 storage system models (exlcuding DX60S2) attached to Windows Server 2008 R2 and earlier Windows operating systems.
The bulletin outlines two methods for reclaiming space on ETERNUS DX S2 storage systems: SDelete and PerfectStorage.
SDelete Offered with a Warning
The widely-known manual method of reclaiming space with SDelete is the first option mentioned. However, the Fujitsu issues a warning for SDelete users:
“Warning: Before executing the sdelete command, please make sure that there is enough free space remaining in the Thin Provisioning Pool to accommodate the extra space required for the LUN’s free space. When sdelete writes zeros to a previously unmapped storage segment the ETERNUS will allocate physical storage from the Thin Provisioned Pool. Pool usage will actually increase when the sdelete command is run.”
Running SDelete in a production environment would cause applications and services to fail, which in turn would lead to an influx of calls to the helpdesk.
SDelete consumes all available free space on the disk, so that space won’t be available to any other application or service. Typically a script must be written to ensure the SDelete command is issued properly. Applications and services need to be shut down.
Also, command line utilities like SDelete are going to do the bare minimum in terms of functionality. There is no automated analysis of your disks telling you how much space you can reclaim, where it resides, and if it even makes sense to deploy your resources to reclaim that space. It’s a guessing game.
Run PerfectStorage to Avoid Unwanted Side Effect of SDelete
Fujitsu recommends PerfectStorage for space reclamation in ETERNUS DX S2 storage systems in order to avoid the “unwanted side effect” of using the SDelete utility:
“There are two options for Space Reclamation offered in this software:
“‘SCSI UNMAP’ option: This is the default method. The SCSI UNMAP command is issued to storage elements which contain non-zero data. The storage elements which contain all zeros allocated to physical storage are not targeted by this software.
“The PerfectStorage Utility also offers the ‘Smart Zero Fill’ option which will write zeros to free areas just as the sdelete option. However, it is careful to only write zeros to the storage areas which do not contain all zeros so the unwanted side effect with sdelete utility is avoided.”
PerfectStorage doesn’t waste resources on clusters that have already been zeroed. This allows PerfectStorage to run in a production environment — no need to shut down applications and services.
PerfectStorage also runs automated disk analyses that report where and how much space can be reclaimed, dramatically cutting the down time required to maintain thin-provisioned storage. The whole process can be customized and automated to run according to the administrator’s preferences.
See Fujitsu’s Bulletin: Space Reclamation in Windows Servers without UNMAP Support