Memory management in QTS

The storage is managed in the “Storage & Snapshots” app, which can be found in the AppCenter. All installed drives are listed in the overview. Before the storage pool and volumes are created, it should be determined which applications are to run on the NAS and what requirements they have.

System drive

The first volume created is of particular importance as this becomes the system drive, on which all installed apps and most of the operating system run by default. For home users, this volume should therefore be on fast (SSD) storage for the best performance. In the example configuration, these are the two M2 SSDs for which the system drive will be created in the next steps.

A storage pool and volume are created in the “Storage” – “Storage / Snapshots” tab and there with “Create” / “New storage pool”.

In the first step only a summary is shown, the option “Activate QTier (automatic storage tiering)” is not necessary for a system drive that is already running on SSDs.

In the second step, the data carriers and the RAID type must be selected from which the storage pool is to be created. Only RAID types 1, 5, 6 (or, if necessary, 10) should be selected here, as this is the only way to easily replace a defective drive.

For SSDs, over-provisioning can be activated in the next step.

After the selected settings have been summarized, the storage pool is created. A warning is displayed that all data on the drives will be deleted; this only relates to the selected drives.

After the storage pool has been created, the first (system) volume is created, the popup message leads directly to the corresponding wizard.

To create a volume, you must first define the storage pool and the type of volume. There are three types available:

  • Static volume – these are the fastest, but later do not offer any extended functions that should no longer be dispensed with in new QNAP NAS models, so these should only be used in special cases
  • Thick volume – A fixed memory area is reserved here and the volume offers the best performance that can be achieved with the full range of functions, so this should normally be selected
  • Thin volume – These behave in a similar way to thick volumes, but only the actually used memory is reserved by the storage pool, which means that more memory can be simulated in volumes than is actually available in the storage pool; this variant, however, requires more maintenance, since considerable problems will arise if the amount of memory is too small

After the storage pool and the type have been determined, the characteristics of the file system must be determined. In addition to the name of the volume, these are above all the size and the bytes per inode.

In the example, the entire available memory of the M2 SSD is to be used as the system drive, so the size is set to the maximum available value. This should not be done with data drives in order to be able to use functions such as snapshots later.

The size of the “Bytes per Inode” must take into account the maximum size and number of files that are later to be stored on the volume. In the case of the system drive, the maximum available 16 TiB is sufficient, since currently only M2 (SATA) SSDs with 4 TiB or 8 TiB are available and therefore the maximum value for 4K cannot be achieved. Likewise, a large number of smaller files can be expected on a system drive, so that the number of files also fits the selection for 4K.

A summary of the settings follows.

With “Finish” the (system) volume is created and a number of (system) shares are created and further apps are added.

Data drives

Data drives that use both HDDs and SSDs can be created as QTier, for this the option “Activate QTier (automatic storage tiering)” must be activated.

The selection of QTier leads to the following differences.

  • The disks to be used are selected for each tier, up to 3 tiers (from HDD, SAS and SSD) are possible, but most models will only offer 2 tiers (from HDD and SSD).
  • Depending on this, 2 or 3 RAID groups are created, which are also shown in a summary.

Initially, the fast tier will be created from SSDs. The following points should be considered when selecting the RAID type.

  • For performance reasons, only RAID groups of the same type should be used in a storage pool.
  • Compared to RAID-5, RAID-6 offers better security against URE errors, in which individual bits can no longer be read, which can lead to the failure of the entire RAID in the event of a rebuild. This is especially true for dives with today’s usual sizes of HDDs.
  • With RAID-10, only certain disks can fail if any other one has already failed, which is a disadvantage compared to RAID-6, in which any second disk can fail.

For normal home servers that do not operate any virtual machines or databases on the NAS, RAID-6 should therefore be used.

Second, the HDDs are then selected. If a SAS tier is available, it should be configured between SSDs and HDDs.

The summary then shows the two (or three) RAID groups with the respective settings.

RAID scrubbing

If RAID-5 or RAID-6 drives have been created, regular RAID scrubbing should be planned for them. This can be done via the global settings at the top right of the “Storage & Snapshots” app.

According to the current status in the QNAP forum, a monthly execution should be sufficient to identify defective sectors of the disks in good time and to be able to replace the affected disks in good time.

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