HP StorageWorks Scalable File Share Release Notes - Version 2.3

New and changed features in HP SFS Version 2.31–20
1.8.2.2 Section 5.7.1 Understanding quota tuning
1.8.2.2.1 OST block quota BTUNE and BUNIT values
With HP-SFS V2.2-1 the per OST block quota allocation bunit default value is 100 MB, and the btune default
value is 50 MB (50 %). With HP-SFS V2.3, the bunit and btune values are function of the number of ll_ost
and ll_ost_io processes running on OSS servers.
limit = <ll_ost_proc_cnt> + <ll_ost_io_proc_cnt> + 10
btune = limit * 1 MB
bunit = btune * 2
The number of ll_ost and ll_ost_io processes depends on the memory size and the the number of CPUs of
the OSS server. Here are some examples of the limit, btune and bunit values for various OSS server
configurations:
The bunit, btune and limit values for OSTs can be retrieved by checking on the OSS nodes the content of
the following files:
• /proc/fs/lustre/obdfilter/<sysname><ost>/quota_btune_sz
• /proc/fs/lustre/obdfilter/<sysname><ost>/quota_bunit_sz
• /proc/fs/lustre/obdfilter/<sysname><ost>/quota_limit_sz
The MDS bunit and btune values remain the same as in HP-SFS V2.2-1, respectively 100 MB and 50 MB.
1.8.2.2.2 Working out user quota
When one sets block quota limits, blocks are granted to OST devices in Units of bunit MB. The MDS also
needs to be granted a small amount of space to hold the data for your files. When a user creates the first
file, the MDS is awarded one 100 MB unit of quota, then the first OST is awarded 1 bunit unit of quota,
then the second, and so on. Therefore, to decide on an appropriate quota value for a user, first decide what
you want the user’s average per-OST number of units to be, then add one unit for the MDS so that:
User Total Quota Limit (KB) = (( <Avg_quota_units_per_ost> * <Num_OSTS> ) * bunit + 100 ) * 1024
Example: OST_BUNIT is 396 MB (Number of ll_ost + ll__ost_io threads is 188 on OSS servers). If you
want a user to have an average usage of 2 GB (approximately 5 units) per OST, and you have an 8 OST
filesystem, then you should assign them a quota of ( (5 * 8) * 396 + 100) * 1024 = 16322560.
1.8.2.2.3 Quota unit allocation
An OST will only return a quota when the usage level of the previous unit of quota drops below the btune
setting.
For example, assuming you are using a quota unit of 100 MB and a tune of 50, the user:
• Can write 1 MB to the OST, so the OST acquires a unit (100 MB) of quota.
• Continues to write to the OST until it is filled to 50MB. At this point, the OST will acquire a second
(100 MB) unit of quota for this user.
• Stops writing to the filesystem after creating 140 MB of files.
• Starts to delete files previously written to the filesystem. When they delete enough files to drop below
the tune watermark of the initial quota unit (below 50 MB used), the OST releases the second quota
unit.
OST server model RAM CPUs ll_ost Procs limit btune bunit
DL360 G4 2 GB 2 124 134 134 MB 268 MB
DL360 G4 3 GB 2 188 198 198 MB 396 MB
DL380 G5 2 GB 4 248 258 258 MB 516 MB