SCSI tape block size
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Hi all
I've got a problem report and a patch from John Adams, he says tmscsim driver under 2.6.17 and on doesn't allow him to read tapes with blocksize of 1MB. He fixes this with the below patch.
scsi/tmscsim.c line 2307
Quoted 12 lines · John Adams
scsi/tmscsim.c renamed from scsi/tmscsim.c.bak +2
-1@@ -2300,7 +2300,8 @@ .this_id = 7, .sg_tablesize = SG_ALL, .cmd_per_lun = 1, - .use_clustering = DISABLE_CLUSTERING, + .use_clustering = ENABLE_CLUSTERING, + .max_sectors = 2048, };/***********************************************************************
It looks like
1) use_clustering doesn't directly affect maximum block size, so, he doesn't really need it, although, it might make sense for tmscsim to improve performance.
2) max_sectors is indeed what he needs, but it looks strange that now it has to be set by the low-level driver... For block devices you can set it at run time with /sys/block/sda/queue/max_sectors_kb, right? But what about tapes?
Sorry, didn't find too much documentation about it.
Thanks
Guennadi
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Guennadi Liakhovetski
Quoted 23 lines · Guennadi Liakhovetski
Hi all
I've got a problem report and a patch from John Adams, he says tmscsim driver under 2.6.17 and on doesn't allow him to read tapes with blocksize of 1MB. He fixes this with the below patch.
scsi/tmscsim.c line 2307
Quoted 12 lines · John Adams
scsi/tmscsim.c renamed from scsi/tmscsim.c.bak +2
-1@@ -2300,7 +2300,8 @@ .this_id = 7, .sg_tablesize = SG_ALL, .cmd_per_lun = 1, - .use_clustering = DISABLE_CLUSTERING, + .use_clustering = ENABLE_CLUSTERING, + .max_sectors = 2048, };/*********************************************************************** It looks like
Quoted 8 lines
1)
use_clusteringdoesn't directly affect maximum block size, so, he doesn't really need it, although, it might make sense for tmscsim to improve performance.2)
max_sectorsis indeed what he needs, but it looks strange that now it has to be set by the low-level driver... For block devices you can set it at run time with/sys/block/sda/queue/max_sectors_kb, right? But what about tapes?
Thank you for posting this. I was wondering why with 2.6.16 the maximum tape block I could access via by BusLogic adapter dropped to 64k. Now I know what to change.
Does anyone know what the appropriate max sectors limit is for BusLogic?
Thanks,
Mike
Quoted 13 lines
Sorry, didn't find too much documentation about it.
Thanks
Guennadi
---
Guennadi Liakhovetski
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Quoted 23 lines · Guennadi Liakhovetski
Hi all
I've got a problem report and a patch from John Adams, he says tmscsim driver under 2.6.17 and on doesn't allow him to read tapes with blocksize of 1MB. He fixes this with the below patch.
scsi/tmscsim.c line 2307
Quoted 12 lines · John Adams
scsi/tmscsim.c renamed from scsi/tmscsim.c.bak +2
-1@@ -2300,7 +2300,8 @@ .this_id = 7, .sg_tablesize = SG_ALL, .cmd_per_lun = 1, - .use_clustering = DISABLE_CLUSTERING, + .use_clustering = ENABLE_CLUSTERING, + .max_sectors = 2048, };/*********************************************************************** It looks like
Quoted 9 lines
1)
use_clusteringdoesn't directly affect maximum block size, so, he doesn't really need it, although, it might make sense for tmscsim to improve performance.2)
max_sectorsis indeed what he needs, but it looks strange that now it has to be set by the low-level driver... For block devices you can set it at run time with/sys/block/sda/queue/max_sectors_kb, right? But what about tapes?
Both 1 and 2 are needed for 1 MB block size. max_sectors_kb for tapes is not visible in /sys.
Quoted 2 lines
Sorry, didn't find too much documentation about it.
The limits come from the block subsystem that all scsi devices use nowadays. It is a rather long story but can be found from linux-scsi archives, e.g.,
http://marc.theaimsgroup.com/?l=linux-scsi&m=114147170831847&w=2
Signature · 1 line
Kai
use_clustering again (was Re: SCSI tape block size)
Quoted 4 lines · Kai Makisara
The limits come from the block subsystem that all scsi devices use nowadays. It is a rather long story but can be found from linux-scsi archives, e.g.,
http://marc.theaimsgroup.com/?l=linux-scsi&m=114147170831847&w=2
Yes, already found the 2 later threads - one on lkml and one on scsi. I did look at them briefly back then, but, probably, too briefly.
One of the settings - enable_clustering - seems to be pretty critical and can only be verified to be safe by intensive testing of various chips / cards. So, how about making it a run-time parameter? A module parameter is the easiest, but then each lld would have to do the same thing more or less. A sysfs attribute - but where? It is a queue attribute, but st/sg don't expose their queues in /sys...
Maybe under /sys/class/scsi_host?
Similar for max_sectors?
Thanks
Guennadi
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Guennadi Liakhovetski
Re: use_clustering again (was Re: SCSI tape block size)
Quoted 11 lines · Guennadi Liakhovetski
Quoted 4 lines · Kai Makisara
The limits come from the block subsystem that all scsi devices use nowadays. It is a rather long story but can be found from linux-scsi archives, e.g.,
http://marc.theaimsgroup.com/?l=linux-scsi&m=114147170831847&w=2Yes, already found the 2 later threads - one on lkml and one on scsi. I did look at them briefly back then, but, probably, too briefly.
One of the settings -
enable_clustering
If you are just trying to get to 1MB, then instead of enabling clustering we could also increase the defaul SCSI_MAX_PHYS_SEGMENTS. It is 128 now, but there is a compile option to set it it up to 256.
Well, actually I think that gets a little short because SG_ALL is only
255. Why is SG_ALL 255, but you can set SCSI_MAX_PHYS_SEGMENTS to 256?
Re: use_clustering again
Quoted 1 line
Quoted 1 line
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"Mike" == Mike Christie <[email protected]> writes:
Mike> If you are just trying to get to 1MB, then instead of enabling Mike> clustering we could also increase the defaul
Mike> SCSI_MAX_PHYS_SEGMENTS. It is 128 now, but there is a compile Mike> option to set it it up to 256.
I have essentially been having the same problem doing big direct I/Os using sg. I ended up bumping sg_tablesize to 1024 but only because I knew the controllers used for this application support that many scatter-gather segments.
As you mention, SG_ALL is 255 and that used to be the max value (quite useless, just short of 1MB). In recent kernels it's been clamped to 128 thanks to getting intimate with the block/request layer.
These short lists are quite useless for contemporary tape hardware that need a block size of 1MB at the minimum and preferably 2MB or more...
Signature · 1 line
Martin K. Petersen Oracle Linux Engineering
Quoted 2 lines · Kai Makisara
Both 1 and 2 are needed for 1 MB block size.
max_sectors_kbfor tapes is not visible in /sys.
Kai, as st maintainer, you surely know - on my tape HP C1533A I cannot seem to set up any block size other than 1 byte... Is it __really__ 1 byte or is it just some fixed block size that the drive doesn't report and cannot change? And it means I cannot test setting of different block sizes? I have a (unconnected ATM) slightly newer C1555D, wonder if that could use different block sizes?...
1 byte I see in "mt status" and setting anything else with "mt setblk" causes "st0: Incorrect block size."
Thanks
Guennadi
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Guennadi Liakhovetski
Quoted 5 lines · Guennadi Liakhovetski
Quoted 2 lines · Kai Makisara
Both 1 and 2 are needed for 1 MB block size.
max_sectors_kbfor tapes is not visible in /sys.
Quoted 7 lines
Kai, as st maintainer, you surely know - on my tape HP C1533A I cannot seem to set up any block size other than 1 byte... Is it
__really__1 byte or is it just some fixed block size that the drive doesn't report and cannot change? And it means I cannot test setting of different block sizes? I have a (unconnected ATM) slightly newer C1555D, wonder if that could use different block sizes?...
This is interesting. I also have HP C1533A (firmware 9608) and I have not had any problems with setting the block size. Dmesg shows that the drive supports blocks up to 1<<24 - 1 bytes:
st0: Block limits 1 - 16777215 bytes.
I just tested with kernel 2.6.18 that setting block size works in my system.
Quoted 3 lines
1 byte I see in "mt status" and setting anything else with "mt setblk" causes "st0: Incorrect block size."
This message comes from reading in fixed block mode when the drive tries to read a block and the size of the block does not match the block size set to the drive. If you have written the tape with block size 1, you can't read it with any other block size in fixed block mode.
If you are testing the limits of the LLD, it may be easier to use variable block mode. What matters is the size of the SCSI i/o and in this case you know it exactly. In fixed block mode the i/o size may be several blocks unless you are careful.
Signature · 1 line
Kai
Quoted 9 lines · Kai Makisara
Quoted 7 lines · Guennadi Liakhovetski
Kai, as st maintainer, you surely know - on my tape HP C1533A I cannot seem to set up any block size other than 1 byte... Is it
__really__1 byte or is it just some fixed block size that the drive doesn't report and cannot change? And it means I cannot test setting of different block sizes? I have a (unconnected ATM) slightly newer C1555D, wonder if that could use different block sizes?...
Quoted 7 lines
This is interesting. I also have HP C1533A (firmware 9608) and I have not had any problems with setting the block size. Dmesg shows that the drive supports blocks up to 1<<24 - 1 bytes:
st0: Block limits 1 - 16777215 bytes.I just tested with kernel 2.6.18 that setting block size works in my system.
I must have done something wrong yesterday. Sorry. It does work indeed, tested with
mt -f /dev/st0 setblk expr $bs \* 1024
time tar cf /dev/st0 -b expr $bs \* 2 *jp*
mt -f /dev/st0 status
I can set block size as high as 512k (.max_sectors defaulting to 1024) independent of .use_clustering. Only setting .max_sectors higher lets one use larger blocks.
Thanks
Guennadi
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Guennadi Liakhovetski