Hello,
It is my opinion, based on information from a Quantum tape
drive engineer and my own experiences with LTO-4 tapes that
you can safely use 256K block sizes. The Quantum guy
confirmed my belief that at larger block sizes you increase the
risk of tape errors. Note: this was back in the days of LTO-4 tapes,
thus it may have changed with the introduction of
LTO-5 and LTO-6 drives.
Some users are trying larger block sizes, but I have seen
many reports of excessive errors at block sizes of 512K and
up.
Best regards,
Kern
On 09/16/2013 01:15 PM, Andreas Koch wrote:
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> On 09/11/2013 04:47 PM, Brian Debelius wrote:
>> Hi,
>>
>> If so what OS, Kernel, SCSI adapter, and LTO drive are you using?
> Scientific Linux 6.4
> Kernel 2.6.32-358.14.1.el6.x86_64
> SAS Adapter IBM 6GB SAS HBA 90Y4579 (using the LSI mpt2 driver 16.00.01.00)
> Drive is HP Ultrium 5-SCSI, firmware Z51U
>
>> What does your bacula-sd.conf look like?
> Here is the relevant excerpt:
>
> Device {
> Name = LTO-5
> Media Type = LTO-5
> Archive Device = /dev/nst0
> AutomaticMount = yes; # when device opened, read it
> AlwaysOpen = yes;
> RemovableMedia = yes;
> RandomAccess = no;
> Maximum File Size = 8g;
> Minimum block size = 131072
> Maximum block size = 131072
> Changer Device = /dev/changer
> AutoChanger = yes
> Alert Command = "sh -c 'smartctl -H -l error /dev/sg11'"
> Maximum Spool Size = 3000g
> Spool Directory = /etc/bacula/spooldisk/BaculaSpool
> Maximum Network Buffer Size = 65536
> }
>
>> What is your drive block size set to?
> No block size has been set using mt setblk/defblksize. But for the current
> backup tape, the data is:
>
> # mt -f /dev/nst0 status
> SCSI 2 tape drive:
> File number=0, block number=0, partition=0.
> Tape block size 32768 bytes. Density code 0x46 (LTO-4).
> Soft error count since last status=0
> General status bits on (41010000):
> BOT ONLINE IM_REP_EN
>
> # tapeinfo -f /dev/nst0
> Product Type: Tape Drive
> Vendor ID: 'HP '
> Product ID: 'Ultrium 5-SCSI '
> Revision: 'Z51U'
> Attached Changer API: No
> SerialNumber: 'HU1324W3HT'
> MinBlock: 1
> MaxBlock: 16777215
> SCSI ID: 3
> SCSI LUN: 0
> Ready: yes
> BufferedMode: yes
> Medium Type: Not Loaded
> Density Code: 0x46
> BlockSize: 32768
> DataCompEnabled: yes
> DataCompCapable: yes
> DataDeCompEnabled: yes
> CompType: 0x1
> DeCompType: 0x1
> BOP: yes
> Block Position: 0
> Partition 0 Remaining Kbytes: 799204
> Partition 0 Size in Kbytes: 799204
> ActivePartition: 0
> EarlyWarningSize: 0
> NumPartitions: 0
> MaxPartitions: 0
>
> Again, the crucial part is that dd can easily handle larger block sizes (we
> tested up to 2 MB). But btape fails with anything larger than 128 KB (see
> log in previous mails).
>
> Best regards,
> Andreas
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