Frequently asked questions about Virtual San/vsan

Q: Vsan needs to use SSD, what's the use of it?

A: SSD is used for read caching (70%) and write Buffering (30%). Each write will go to SSDs first, and then cancel the staging to the HDD later.

Q: When you create a VSAN virtual machine storage Policy, when should you use the "allowed number of failures", when should use "stripe width".

A: The number of allowed failures is related to availability, and you can define this policy if you need to keep the virtual machine available when a host or disk group fails. Therefore, if 1 host failures are allowed, the policy can be defined as 1. This creates 2 data objects and a witness in the cluster. Stripe width is related to performance (that is, read performance when not in the cache, and cancellation of write staging). A value set to 2 or higher causes the data to be striped across multiple disks. If used in conjunction with the number of allowed failures, the data in a virtual machine may be stored on multiple disks on multiple hosts.

Q: Does Vsan have a default storage policy?

A: Yes, all virtual machines on the Vsan data store apply a default policy, but you do not see the policy in the vsphere UI. You can see by using the following command that the default policy is defined as a different class: Esxcli Vsan policy Getdefault. The "Allow n+1 number of failures" policy is applied by default, so that even if the user forgets to create and set policies, the object is also capable of recovery. It is recommended that you do not change the default policy.

Q: After setting the stripe width to 2, the data is striped across multiple disks on the host.

A. First, setting the stripe width to 2 does not guarantee that the data will be striped across multiple disks on a host. VSAN's own algorithm determines where the data should be placed, so while all hosts have enough disks, the data may still be striped across multiple hosts rather than striped across multiple disks in a host. Data stripe is done in blocks of 1MB.

Q: Since VSAN will create a data store, what is the purpose of "disk Group"?

A: The disk group can be defined SSD,SSD in front of a group of HDD for caching/buffering. In general, a disk group is a way to map an HDD to an SSD. Each disk group has 1 SSD and up to 6 disks. Based on customer feedback, we plan to increase the HDD to 7 so that a disk group can be built on a host with 8 Physical disk slots.

Q: How many disks can a single host provide for VSAN?

A: Up to 5 disk groups, 1 SDD per disk group and at least 1, up to 6 HDD. The maximum number of HDD per host is 5 x 6 = 30. The maximum number of SSD per host is 5 x 1 = 5.

Q: Can I support both SSD and PCIe flash cards?

A: Yes, both can be supported at the same time. However, please check the HCL for details, as there are some guidelines and requirements to note.

Q: Does the Vsan have to use 10GbE?

A: VSAN does not enforce the requirement to use 10GbE. Vsan can also work well with 1GbE in smaller environments, such as in the lab. Please note that 10GbE is a recommended value.

Q: Why is it recommended to configure the quarantine response for HA to "Powered-off (closed)"?

A: When VSAN is enabled, vsphere ha uses the VSAN vmkernel network to implement the heartbeat. If the host does not receive any heartbeat, from the VSAN point of view, it is likely that the host has been separated/partitioned from the rest of the cluster. In this case, it is recommended that the virtual machine be powered down because HA automatically opens a new copy of the Power on the remaining hosts in the cluster. Thus, when the host is out of quarantine, 2 virtual machines with the same identity are not present in the network.

Q: Can I partition SSD or disk and use them in other ways (for example, install Esxi/vflash).

A: No, you cannot partition SSD or HDD. A Virtual SAN will always occupy the entire disk. The most feasible way to use VSAN may be to install ESXi on an internal USB/SD card, which maximizes the capacity of the VSAN.

Q: VSAN support to repeat or compress it.

A: The current version of VSAN does not support duplication or compression. In VSAN clusters, the most expensive resource is the ssd/flash, so data duplication is most likely to occur on this layer. If the data has multiple replicas, there will be two replicas on the HDD, and a distributed write buffer (SSD 30%) will have two temporary copies, while the distributed read cache portion of the flash memory (70%) Only one copy is included for any cached data.

Q: Can vsan use San/nas data storage?

A: VSAN currently does not support the use of San/nas data storage. The disk must be "local" and passed directly to the host.

Q: Some people say that if I set object space reservation to 100%, the disk will be streamlined by default VSAN. Does this mean that the VMDK will become a thick provisioning zero?

Answer: No. The definition of "object space reservation" does not imply a virtual opportunity for thick provisioning or partial thick provisioning. If you use "used disk space/free disk space" to calculate, the object space reservation is entirely related to the quantity used by VSAN. If you set object space reservation to 100% on a 25GB disk, the disk becomes a compact provisioning disk, but Vsan assumes that 25GB has a space of 100% to compute. I think it can be compared to memory reservations.

Q: Vsan will use ISCSI or NFS to connect hosts to the data store.

A: VSAN does not use either of these to connect the host to the data store. It will use a proprietary mechanism.

Q: What is the impact of the maintenance mode on the VSAN cluster enabled?

A. For hosts that provide storage for VSAN data storage, you can put them in maintenance mode in three ways:
1 Full data Migration – migrate all data on the host. Impact: It may take a long time to complete.
2 Ensure accessibility –vsan keep all virtual machines accessible by migrating the necessary data to other hosts. Impact: Possible violation of availability policy.
3 No Data migration – no data is migrated. Impact: Depending on the number of allowed failures policy defined, some virtual machines may not be available.
The safest option is option 1, and option 2 is the preferred and default option because the fastest completion. I think the problem is why you put the host in maintenance mode and how long the host can use again. If you do need to enter maintenance mode quickly and do not care that data may be lost, you can choose option 3: Fallback.

Q: Does the vsphere have VSAN or incompatible features?

A: Currently, VSAN does not support vsphere distributed power Management, Storage DRS, and Storage IO control.

Q: How do I add a Virtual San/vsan license?

A: The VSAN license is applied at the cluster level. Open the Web Client, click the cluster that is enabled for VSAN, and then click the Manage tab and the settings. Under Configuration, click Virtual San Licensing (Virtual sans license), and then click Assign License Key (assign license key).

Q: How is a Virtual SAN priced/licensed?

A: VSAN will be licensed by slot, but the pricing details have not yet been disclosed. Note that the current VSAN Beta license code includes DVS and virtual machine storage policies, even with vsphere licenses that are lower than Enterprise Plus.

Q: If the host fails, resulting in data loss, and all virtual machines are protected by the n+1 policy, how long will it take for VSAN to begin rebuilding the lost data?

A: VSAN determines which objects (that is, objects protected by the n+1 policy and stored in the host) are not compliant, and then starts a 60-minute timeout period. This timeout period is intended to avoid unnecessary and costly full data synchronization. If the host recovers within 60 minutes, the resulting variance is replicated to the host. If the virtual machine has multiple mirrors and does not notice the failure, the 60-minute period will revert to full policy compliance, which can be used to cope with more failures.

Q: When a virtual machine moves in a cluster, does its object move along with it so that IO remains local.

A: No, objects, such as virtual disks, do not move along with the virtual machine. Just imagine what the cost/cost of moving a virtual disk between hosts is known each time the DRS recommends a migration. At this point, IO can be executed remotely. This means that although the virtual machine may be running on Host 1 from the cpu/memory point of view, its virtual disk might actually be on host 2 and host 3.

Q: After a virtual machine migrates to another host, if the vMotion is executed, will the SDD cache (temporarily affect performance) be lost, and the cache will be incrementally rebuilt.

A: There is no loss of cache and no need to rebuild/re-enable caching. If necessary, the cache can be accessed remotely.

Q: VSAN support Fault tolerance (that is, FT).

A: Not supported, this version of VSAN does not support Fault tolerance.

Q: In Sphere, the SSD in the host is reported as "non-SSD". According to technical support, this issue is a known issue with the version of the server you are using. Does the disk type "false positives" have an impact on the configuration of the VSAN?

Answer: Yes. You need to mark the SSD as local using the correlation identifier (The following example is used in my lab and may be different from your identifier). Here, I set it for "local" and "SSD".
ESXCLI storage nmp SATP rule ADD–SATP vmw_satp_local–device mpx.vmhba2:c0:t0:l0–option "Enable_local ENABLE_SSD"

Q: As mentioned above, after a failure, it takes 60 minutes for VSAN to begin automatic repair. Can you shorten this timeout value?

A: * * Disclaimer: It is not recommended to change this value, and I am not sure if I support this change *
Yes, you can configure the name "VSAN" on each host in the VSAN cluster. Clomrepairdelay to shorten the timeout value.

Q: Why not use the data store heartbeat feature in only VSAN clusters.

A: There is no requirement for detection signal data storage. This feature is not available only in the case of VSAN data storage because HA uses the VSAN network to implement the heartbeat. Therefore, if the host is isolated from the VSAN network and cannot send a heartbeat, it is certain that the host cannot remotely update the heartbeat area, so that it is meaningless to enable this feature in only VSAN environments.

Q: What are the specific best practices for deploying View on VSAN?

A: Yes, mainly for availability/caching and capacity reservation. Andre Leibovici wrote a good article on this subject and read it now. (http://myvirtualcloud.net/?p=5440)

Q: Can the VSAN vmkernel of a host in a cluster belong to another subnet?

A: VSAN Vmkernel must belong to the same subnet. One (or more) hosts in a VSAN cluster are not supported on different subnets. If multiple Vmkernel interfaces are used for each host, each interface must belong to a different subnet.

Q: VSAN support spans multiple geographic locations.

A: The current version of VSAN does not support a "metropolitan" cluster.

Q: What is the difference between a host failure and a gradual disk failure?

A: There really is a difference. There are a number of failure states, and depending on these states, you can also determine how quickly VSAN starts a new mirror. Two of these failed states are "non-existent" and "degraded." Degraded refers to a disk failure and the system has recognized the failure and is aware that the disk has not been recovered. In this case, VSAN recognizes this "degraded" state and immediately creates a new mirror image for the affected object, since it is not necessary to wait 60 minutes if the disk is known to not recover quickly. The "No" status means that VSAN does not know if the disk will recover quickly, either the host fails or a disk is suddenly moved, and the system starts a 60-minute timeout.

Q: What happens if SSD fails in the VSAN cluster?

A: SSD is in front of the disk group and acts as a read cache/write buffer. If the SSD fails, the disk group and all the components it stores are marked as degraded. Then, if you have enough disk capacity, VSAN will create a new mirrored copy, if appropriate. For more information, please read the http://www.yellow-bricks.com/2013/09/18/vsan-handles-disk-host-failure/

Q: Does vsphere support TRIM on SSD?

A: Not supported, currently does not support trim, and will not use trim.

Q: Vsan needs to use SSD, what's the use of it?

A: SSD is used for read caching (70%) and write Buffering (30%). Each write will go to SSDs first, and then cancel the staging to the HDD later.

Q: When you create a VSAN virtual machine storage Policy, when should you use the "allowed number of failures", when should use "stripe width".

A: The number of allowed failures is related to availability, and you can define this policy if you need to keep the virtual machine available when a host or disk group fails. Therefore, if 1 host failures are allowed, the policy can be defined as 1. This creates 2 data objects and a witness in the cluster. Stripe width is related to performance (that is, read performance when not in the cache, and cancellation of write staging). A value set to 2 or higher causes the data to be striped across multiple disks. If used in conjunction with the number of allowed failures, the data in a virtual machine may be stored on multiple disks on multiple hosts.

Q: Does Vsan have a default storage policy?

A: Yes, all virtual machines on the Vsan data store apply a default policy, but you do not see the policy in the vsphere UI. You can see by using the following command that the default policy is defined as a different class: Esxcli Vsan policy Getdefault. The "Allow n+1 number of failures" policy is applied by default, so that even if the user forgets to create and set policies, the object is also capable of recovery. It is recommended that you do not change the default policy.

Q: After setting the stripe width to 2, the data is striped across multiple disks on the host.

A. First, setting the stripe width to 2 does not guarantee that the data will be striped across multiple disks on a host. VSAN's own algorithm determines where the data should be placed, so while all hosts have enough disks, the data may still be striped across multiple hosts rather than striped across multiple disks in a host. Data stripe is done in blocks of 1MB.

Q: Since VSAN will create a data store, what is the purpose of "disk Group"?

A: The disk group can be defined SSD,SSD in front of a group of HDD for caching/buffering. In general, a disk group is a way to map an HDD to an SSD. Each disk group has 1 SSD and up to 6 disks. Based on customer feedback, we plan to increase the HDD to 7 so that a disk group can be built on a host with 8 Physical disk slots.

Q: How many disks can a single host provide for VSAN?

A: Up to 5 disk groups, 1 SDD per disk group and at least 1, up to 6 HDD. The maximum number of HDD per host is 5 x 6 = 30. The maximum number of SSD per host is 5 x 1 = 5.

Q: Can I support both SSD and PCIe flash cards?

A: Yes, both can be supported at the same time. However, please check the HCL for details, as there are some guidelines and requirements to note.

Q: Does the Vsan have to use 10GbE?

A: VSAN does not enforce the requirement to use 10GbE. Vsan can also work well with 1GbE in smaller environments, such as in the lab. Please note that 10GbE is a recommended value.

Q: Why is it recommended to configure the quarantine response for HA to "Powered-off (closed)"?

A: When VSAN is enabled, vsphere ha uses the VSAN vmkernel network to implement the heartbeat. If the host does not receive any heartbeat, from the VSAN point of view, it is likely that the host has been separated/partitioned from the rest of the cluster. In this case, it is recommended that the virtual machine be powered down because HA automatically opens a new copy of the Power on the remaining hosts in the cluster. Thus, when the host is out of quarantine, 2 virtual machines with the same identity are not present in the network.

Q: Can I partition SSD or disk and use them in other ways (for example, install Esxi/vflash).

A: No, you cannot partition SSD or HDD. A Virtual SAN will always occupy the entire disk. The most feasible way to use VSAN may be to install ESXi on an internal USB/SD card, which maximizes the capacity of the VSAN.

Q: VSAN support to repeat or compress it.

A: The current version of VSAN does not support duplication or compression. In VSAN clusters, the most expensive resource is the ssd/flash, so data duplication is most likely to occur on this layer. If the data has multiple replicas, there will be two replicas on the HDD, and a distributed write buffer (SSD 30%) will have two temporary copies, while the distributed read cache portion of the flash memory (70%) Only one copy is included for any cached data.

Q: Can vsan use San/nas data storage?