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Operating Systems AIX IBM AIX Internal HDD vs SAN HDD and Oracle Post 302883312 by rbatte1 on Monday 13th of January 2014 09:11:47 AM
Old 01-13-2014
We have seen differences in performance of a similar scale and nature.

Internal/local disk is managed by your server and it is responsible for all the real IO, writing the bits to the disk controllers and getting the acknowledgement when the update is made to the brown-spinning part.

With SAN storage, the request by your OS to write data is accepted and confirmed by the SAN before the data is really written to disk. It's written to the SAN cache, but as far as your OS is concerned, then transaction is complete and processing can continue.


A SAN disk array will have a large cache dedicated to holding write requests and flushing them to real disk in large IO writes. This is why all SAN disk arrays will have batteries to keep the cache alive in the event of a power failure. This is in addition to any UPS you may have in place. A SAN shutdown can also be done in two ways roughly described as immediate and controlled. In the controlled shutdown, the cache is flushed and the SAN disk is consistent. An Immediate shutdown does not flush the cache and is quicker. It has no difference for the actual data stored unless the battery fails or is replaced.


As to a way to measure it, I suppose you are into creating a large complex file and copying it about a few times. By complex, I mean something that compression software will not easily deal with. My way to do this (mainly for testing FTP speed) is to tar up some large files and compress them, then append them a few times to get the size big enough.

If your hardware can support it, then it can be beneficial to have everything as SAN storage, including the OS and paging space. The limitation then becomes the connection speed to the SAN.

If you replicate your SAN to another site, then this takes care of updates to the boot disks / rootvg / vg00 (whatever you want to call it) that may affect the DR position. Of course, the IP address will be replicated so you have to handle that along with a process to use perhaps different hardware at the remote site.

It is, however no substitute for backups as errors / corruption will also be replicated honestly.



I hope that this helps.

Robin
Liverpool/Blackburn
UK
 

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HTCACHECLEAN(8) 						   htcacheclean 						   HTCACHECLEAN(8)

NAME
htcacheclean - Clean up the disk cache SYNOPSIS
htcacheclean [ -D ] [ -v ] [ -t ] [ -r ] [ -n ] -ppath -llimit htcacheclean [ -n ] [ -t ] [ -i ] -dinterval -ppath -llimit SUMMARY
htcacheclean is used to keep the size of mod_disk_cache's storage within a certain limit. This tool can run either manually or in daemon mode. When running in daemon mode, it sleeps in the background and checks the cache directories at regular intervals for cached content to be removed. You can stop the daemon cleanly by sending it a TERM or INT signal. OPTIONS
-dinterval Daemonize and repeat cache cleaning every interval minutes. This option is mutually exclusive with the -D, -v and -r options. To shutdown the daemon cleanly, just send it a SIGTERM or SIGINT. -D Do a dry run and don't delete anything. This option is mutually exclusive with the -d option. -v Be verbose and print statistics. This option is mutually exclusive with the -d option. -r Clean thoroughly. This assumes that the Apache web server is not running (otherwise you may get garbage in the cache). This option is mutually exclusive with the -d option and implies the -t option. -n Be nice. This causes slower processing in favour of other processes. htcacheclean will sleep from time to time so that (a) the disk IO will be delayed and (b) the kernel can schedule other processes in the meantime. -t Delete all empty directories. By default only cache files are removed, however with some configurations the large number of directo- ries created may require attention. If your configuration requires a very large number of directories, to the point that inode or file allocation table exhaustion may become an issue, use of this option is advised. -ppath Specify path as the root directory of the disk cache. This should be the same value as specified with the CacheRoot directive. -llimit Specify limit as the total disk cache size limit. The value is expressed in bytes by default (or attaching B to the number). Attach K for Kbytes or M for MBytes. -i Be intelligent and run only when there was a modification of the disk cache. This option is only possible together with the -d option. EXIT STATUS
htcacheclean returns a zero status ("true") if all operations were successful, 1 otherwise. Apache HTTP Server 2008-05-06 HTCACHECLEAN(8)
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