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H_Sharma's avatar
H_Sharma
Level 6
10 years ago

SCSI Reserve and Mount Point

Hello Experts,

Pls help with the 2 points.

1)Difference between SPC-2 SCSI reserve and SCSI persistent reserver. What are these?

2) Lets say we have two mount points in backup selection with multistream enabled in backup selection and in Policy.
   \exchange, \firewall now we exclude this firewall mount point directory in exclude_list.
So what will happen. Job for firewall would start or get failed? How many jobs would run?

 

Thanks,

7.6
Backing Up
Backup and Recovery
Basics
NetBackup
Windows Server (2003-2008)
  • mph999's avatar
    mph999
    10 years ago

    Number 2, you can research yourself, give it a go, and report back what you find.

    Number 1 I will help with, again you can also check the guides.

    SCSI SPC-2 reserve is quite basic - a reservation is just put on the drive, for example by media server1.  This prevents any other HBA from making a reservation on the drive (yes reservations 'come' from the HBA, so the drive is therefrore reserverd.  The only way for the reservation to be released is for a scsi reservation release to be sent to the drive, from the same HBA, or by powercycling the drive.

    This is fine, apart from if say you had a cluster and the machine using the drive fails.  Another machine takes over but cannot release the drive, as this can only be done by the original HBA.

    Persistent  is more advanced, basically a reservation key is used, which using various utilities can be read from the drive itself - it looks like this:

    dr-media1:/usr/openv/netbackup/logs/bptm # sg_persist --read-reservation -d /dev/sg5
      IBM       ULT3580-TD5       0103
      Peripheral device type: tape
      PR generation=0xb, Reservation follows:
        Key=0x1d00006001e8488
        scope: LU_SCOPE,  type: Exclusive Access

    The main difference with this, is that if the key is read, it can be determined 'who' set the reservation.   I'm not sure how, but I am told Engineering are able to determine if NBU 'made' the key.  WHat this means is that if the original server, say media server1 set the reservation, a different media server can release it, providing NBU made the reservation. 

  • Marianne's avatar
    Marianne
    10 years ago

    Please read through the section in the manual that I have referred to above.

    There is a section under this topic:

    Recommended use for Enable SCSI reserve property

    You will see that SCSI persistent reserve is especially important in your environment where your clustered master server nodes have tape drives attached.
    You recently posted when there were issues with tape drives after master server failover.

    To know if your tape drives support SCSI persistent reserve, check the NBU HCL:  http://www.symantec.com/docs/TECH76495

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  • Marianne's avatar
    Marianne
    Level 6
    10 years ago
    1) No disrespect, but have you tried to search Admin Guide I? The place I will look for the answer is in Host Properties section under 'Media Properties ' heading. 2) Test this and tell us. This looks like exam type questions, right?
  • mph999's avatar
    mph999
    Level 6
    10 years ago

    Number 2, you can research yourself, give it a go, and report back what you find.

    Number 1 I will help with, again you can also check the guides.

    SCSI SPC-2 reserve is quite basic - a reservation is just put on the drive, for example by media server1.  This prevents any other HBA from making a reservation on the drive (yes reservations 'come' from the HBA, so the drive is therefrore reserverd.  The only way for the reservation to be released is for a scsi reservation release to be sent to the drive, from the same HBA, or by powercycling the drive.

    This is fine, apart from if say you had a cluster and the machine using the drive fails.  Another machine takes over but cannot release the drive, as this can only be done by the original HBA.

    Persistent  is more advanced, basically a reservation key is used, which using various utilities can be read from the drive itself - it looks like this:

    dr-media1:/usr/openv/netbackup/logs/bptm # sg_persist --read-reservation -d /dev/sg5
      IBM       ULT3580-TD5       0103
      Peripheral device type: tape
      PR generation=0xb, Reservation follows:
        Key=0x1d00006001e8488
        scope: LU_SCOPE,  type: Exclusive Access

    The main difference with this, is that if the key is read, it can be determined 'who' set the reservation.   I'm not sure how, but I am told Engineering are able to determine if NBU 'made' the key.  WHat this means is that if the original server, say media server1 set the reservation, a different media server can release it, providing NBU made the reservation. 

  • Marianne's avatar
    Marianne
    Level 6
    10 years ago

    Please read through the section in the manual that I have referred to above.

    There is a section under this topic:

    Recommended use for Enable SCSI reserve property

    You will see that SCSI persistent reserve is especially important in your environment where your clustered master server nodes have tape drives attached.
    You recently posted when there were issues with tape drives after master server failover.

    To know if your tape drives support SCSI persistent reserve, check the NBU HCL:  http://www.symantec.com/docs/TECH76495

  • mph999's avatar
    mph999
    Level 6
    10 years ago

    Please note that some VTLs in particular do NOT like Persistent reserve, and there is a very high risk of data loss.

    I've also seen issues on Solaris with Persistent reserve.

  • H_Sharma's avatar
    H_Sharma
    Level 6
    10 years ago

    We have set our media servers master servers as spc-2. Is there anything that needs to be done to change it to SCSI persistance?

    I mean if i check the SCSI persistance on properties all is it done or need to make change from somewhere else as well?

  • Marianne's avatar
    Marianne
    Level 6
    10 years ago
    Scsi-2 reservation is enabled by default. Before you change it in Host Properties of each media server, check the HCL to see if your make/model tape drives support Persistent reservation.
  • mph999's avatar
    mph999
    Level 6
    10 years ago

    Yes ....

    All devices that see a drive MUST use the same type of reservation (for example, different media servers with SSO, NDMP filers ).  If two different devices share a drive and use different reservation, you will for 100% certain get data loss.

    Also, when changing reservation type, run backups and restores to test - as mentioned, sometimes particular devices are not compatible (even when the OS compatability suggests they are).  VTLs in particular can play up, and I had a case where Solaris media servers didn't want to play nicely.

  • Marianne's avatar
    Marianne
    Level 6
    10 years ago

    I so wish that users will post all relevant details of their environment when they start new discussions - unless the question is asked out of curiosity or to prepare for exam and there is no intention to actually apply in production environment....

    We know from previous posts that there is a Windows clustered master server in this environment with tape drives attached.
    We also know from previous posts that there are 2 Solaris media servers in this environment.
    We do not know anything about the actual tape drives as Inquiry string was removed when output was posted in Scan Command .
    We know that there are no VTLs in this environment.

    So, from what we know, we cannot tell you if you should or should not enable persistent SCSI reserve.

    From the documentation, it is clear that persistent SCSI reserve is a good idea in a clustered environment.
    Martin says that he has seen problems with persistent SCSI reserve on Solaris, but I have personally implemented the setting at a customer site with shared IBM tape drives, clustered Solaris master/media servers, about 6 other Solaris media servers and 2 Windows media servers.
    Because we know nothing about the tape drives, only you can check the HCL for compatibility.

    So, in closing - 
    Only you can decide based on the information you have.

    But I strongly recommend that you first address and solve the issue with 'disappearing' drives before making SCSI reservation changes.

  • mph999's avatar
    mph999
    Level 6
    10 years ago

    If it is clustered and if the drives are attached to machines on both sides of the cluster than persistent reservation should be used.  Why, because if the drives are in use when one side goes down they will be reserved, and the machine that takes over will be unable to break the reservation, meaning the drives will have to be powercycled.

    If persistent reservation is used, then a reservation key comes into play, meaning quite simply that NBU knows it's a NBU reservation key and can break the reservation.

    Personally, I prefer persistent, because the reservation key can be used for troubleshooting, at least on Linux as the sgutils package can be used to read the key off the drive and therefore in the event of reservation errors we can show it's not us causing the issue.

     

     

  • H_Sharma's avatar
    H_Sharma
    Level 6
    10 years ago

    Hi Marianne,

    Master server is on Window 2008 R2, Media servers are on Solaris 11 and Library is Oracle Storagetek SL150.

    I think this is the problem in our environment because every time cluster fails over other node has some issue either 98 error codes. Sometime network errors 13, 41.

    But not sure whether our SL 150 supports SPR.

    Flipping through Library manual and HCL.