Thursday, 27 June 2013

How Mac handle hot cluster zone?

Fragmented hard drive is not rare problem , it occurs over a period of time in every hard drive in installed OS. When you save, delete, write several files in hard drive, empty space are created which is responsible for the scattered data over Mac disk. When you save new data and if it is larger than empty space , OS X keeps it into noncontinuous memory in hard drive. But, some OS like Mac OS X has the capability to prevent fragmentation by using some safety guards so that, users will never feel about the situation of their Mac hard drive.

Mac OS X has new file system i.e HFS+ which has ability to decrease the chance of file fragmentation in Mac drive. If the size of the file is 20MB and it has less than 8 fragments then OS X defrags all these types of files automatically. Another option is 'Hot File Adaptive clustering' which monitors frequently-accessed files between OS and hard drive, and then moves these files to a special zone called Hot File Adaptive clustering on the hard drive. Mac OS X defragments these files at the time of transferring into hot Zone. OS X has faster communication with this Hot Zone and it helps to keep your Mac optimized.

Hot File Clustering (HFC) aims to increase the performance of small, frequently accessed files from Mac volumes. This process is currently used only on boot volumes. HFC is a multi-staged clustering scheme that keeps record "hot" files on a volume, and moves them to the "hot space" on the volume . The various stages in this scheme are DISABLED, IDLE, BUSY, RECORDING, EVALUATION, EVICTION, and ADOPTION. Only files less than 20 MB in size are "adopted" under this scheme.

Note - Hot files on your system will depend on usage pattern in your Mac from last few days. If you are doing extensive C programming from a week then it is likely that many of your hot files will have C headers.

Inspite of all these , there are some circumstances occurs in which you need some third party tool to defrag your Mac:-

1. When you have big large files such as video files in your hard drive.

2. When your Mac hard drive gets completely filled and it has less than 10% free space.

In both above mentioned situations, the built in safeguards of Mac OS fails to prevent defragmentation, and it results sluggish behaviour of their Mac machine . Stellar Drive Defrag is one of the famous Mac defragmentation tool among Mac people. It helps to defrag your entire Mac or any selected file. Through Free version of this tool, you can check the status of your Mac drive, how much it is defragmented.

Paid version of this tool has many advance features like you can see the temperature fluctuation in Mac hard drive with the help of temperature bar. You can see the status of fragmented data free space and filled disk with graphical representation. Defragmentation is a time taking process so, this tool has an option through which you can set email notification/sound to make sure that defragmentation process completed successfully.

Features of Stellar Drive Defrag:-

1. It defrags your Mac without the risk of data loss

2. It helps to improve your Mac performance

3. Temperature bar to show the fluctuations in the temperature of Mac hard drive.

4. Email notification option

5. It supports Hot File Adaptive Clustering.

Apple has many scheme to keep your Mac faster:-

Boot cache:-

Mac OS X has a boot-time optimization which monitors the pattern of incoming read requests to the boot disk, and sorts the request pattern into a "playlist", which is used to cluster reads into a private cache. This "boot cache" is then used for satisfying incoming read requests fastly, if possible. The scheme also measures the cache hit rate, and stores the request pattern into a "history list" for use in future. If the hit rate is low then caching is disabled.

This feature is only supported for root device and it requires minimum 128 MB of physical RAM for enabling it. Entire process remains invisible from users. /System/Library/Extensions/BootCache.kext is the location of the kernel extension.

Helping Developers Create Faster Code:-

Apple provides number of performance measurement/debugging tools for Mac OS X. Some of these you can get with Mac OS and for other tools you need to download from Aple site.

Journaling in HFS Plus:-
On a journaled HFS Plus Mac volume, file object metadata and volume structures are journaled, but file object data are not journaled. The primary purpose of the journal is to make recovery process faster and reliable, in case a volume is unmounted , it helps to improve the performance of metadata operation.

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