C 5-6 Disk

[Claribel Szwaja]

Disk storage (also sometimes called drive storage) is a data storage mechanism based on a rotating disk. The recording employs various electronic, magnetic, optical, or mechanical changes to the disk's surface layer. A disk drive is a device implementing such a storage mechanism. Notable types are hard disk drives (HDD), containing one or more non-removable rigid platters; the floppy disk drive (FDD) and its removable floppy disk; and various optical disc drives (ODD) and associated optical disc media.

Audio information was originally recorded by analog methods (see Sound recording and reproduction). Similarly the first video disc used an analog recording method. In the music industry, analog recording has been mostly replaced by digital optical technology where the data is recorded in a digital format with optical information.

The first commercial digital disk storage device was the IBM 350 which shipped in 1956 as a part of the IBM 305 RAMAC computing system. The random-access, low-density storage of disks was developed to complement the already used sequential-access, high-density storage provided by tape drives using magnetic tape. Vigorous innovation in disk storage technology, coupled with less vigorous innovation in tape storage, has reduced the difference in acquisition cost per terabyte between disk storage and tape storage; however, the total cost of ownership of data on disk including power and management remains larger than that of tape.[1]

Data on modern disks is stored in fixed length blocks, usually called sectors and varying in length from a few hundred to many thousands of bytes. Gross disk drive capacity is simply the number of disk surfaces times the number of blocks/surface times the number of bytes/block. In certain legacy IBM CKD drives the data was stored on magnetic disks with variable length blocks, called records; record length could vary on and between disks. Capacity decreased as record length decreased due to the necessary gaps between blocks.

Digital disk drives are block storage devices. Each disk is divided into logical blocks (collection of sectors). Blocks are addressed using their logical block addresses (LBA). Read from or writing to disk happens at the granularity of blocks.

Originally the disk capacity was quite low and has been improved in one of several ways. Improvements in mechanical design and manufacture allowed smaller and more precise heads, meaning that more tracks could be stored on each of the disks. Advancements in data compression methods permitted more information to be stored in each of the individual sectors.

The drive stores data onto cylinders, heads, and sectors. The sectors unit is the smallest size of data to be stored in a hard disk drive and each file will have many sectors units assigned to it. The smallest entity in a CD is called a frame, which consists of 33 bytes and contains six complete 16-bit stereo samples (two bytes two channels six samples = 24 bytes). The other nine bytes consist of eight CIRC error-correction bytes and one subcode byte used for control and display.

The information is sent from the computer processor to the BIOS into a chip controlling the data transfer. This is then sent out to the hard drive via a multi-wire connector. Once the data is received onto the circuit board of the drive, they are translated and compressed into a format that the individual drive can use to store onto the disk itself. The data is then passed to a chip on the circuit board that controls the access to the drive. The drive is divided into sectors of data stored onto one of the sides of one of the internal disks. An HDD with two disks internally will typically store data on all four surfaces.

The hardware on the drive tells the actuator arm where it is to go for the relevant track and the compressed information is then sent down to the head which changes the physical properties, optically or magnetically for example, of each byte on the drive, thus storing the information. A file is not stored in a linear manner, rather, it is held in the best way for quickest retrieval.

Mechanically there are two different motions occurring inside the drive. One is the rotation of the disks inside the device. The other is the side-to-side motion of the head across the disk as it moves between tracks.

Track positioning also follows two different methods across disk storage devices. Storage devices focused on holding computer data, e.g., HDDs, FDDs, Iomega zip drives, use concentric tracks to store data. During a sequential read or write operation, after the drive accesses all the sectors in a track it repositions the head(s) to the next track. This will cause a momentary delay in the flow of data between the device and the computer. In contrast, optical audio and video discs use a single spiral track that starts at the inner most point on the disc and flows continuously to the outer edge. When reading or writing data there is no need to stop the flow of data to switch tracks. This is similar to vinyl records except vinyl records started at the outer edge and spiraled in toward the center.

The disk drive interface is the mechanism/protocol of communication between the rest of the system and the disk drive itself. Storage devices intended for desktop and mobile computers typically use ATA (PATA) and SATA interfaces. Enterprise systems and high-end storage devices will typically use SCSI, SAS, and FC interfaces in addition to some use of SATA.

While I'm using my computer normally without touching anything Dropbox related, the Dropbox process (I have a system monitor installed that shows disk usage and which process is using it the most among other things) randomly and strangely frequently uses large amounts of my HDD's processing capacity to a point where it causes stuttering in video playback, video games, and other applications that have higher priority for my computer use. This was also verified by simply shutting down Dropbox, since the problem goes away with that.

Since I'm the only user of this account as well, I'm the only one causing changes to it, so there's no new files being received or files being modified which are pushed to me to cause any of this either.

I presume this is Dropbox scanning the folders for changes, but I don't think it should cause this much disk activity or at least not such huge spikes for it. And I'm fairly sure the OS has file system notification API (change notifications, like Linux has inotify) that would remove the need to scan the file system for changes in such old fashioned and resource intense manner.

Also I have same problem. I think thats happen because of keeping lots of files on dropbox. If you changing anything on that folder(s), then dropbox go crazy for trying index operation. Dropbox should change indexing structure...

I've found Dropbox to be the no 1 cause of "beachballing" on my MacBook Pro. With Dropbox active on an account it adds at least a minute or two of waiting before the mac is usable after login, and the computer is literately unusable for other tasks whenever the Dropbox-process is trying to do anything. If I disable Dropbox, performance is back to normal. I can perform heavy I/O operations such as recursive copying of directory-trees with hundreds of gigabytes of data from one drive to another, or to/from a local server, with next to no impact on application/desktop performance, so it makes little sense for Dropbox to completely clog the system to do its job.

As most with a PA-220 have experienced, regardless version running (currently latest 10.2.3-h2) root partition fills up all the time and have to run the disk-usage cleanup commands manually and tried enabling aggressive-cleaning as well, it just continuously hits level/ But it just fills up all the effin time:-)

With the root disk issues seemingly persistent (since at least the high 9 versions) and with the PA-220 only containing a measly 32GB, apart from the disk issues we are perfectly happy with the PA-220 and have a handful across our network, so does anyone know if there is a storage upgrade option? just want to be able to have a bigger eMMC storage in it if possible, either by buying and installing or any Palo support routes that would enable a swap of storage?

Yes thanks, but I've already read those links and others several times as I'm sure everyone else has who is frustrated at the root space issue, as I said in the post we have aggressive cleaning enabled and it hits the 95% threshold several times a day, as I also said above we have ran the disk-usage cleanup command several times with threshold of 90 but it can never make more than 93% free.

Coming with such a small eMMC is so disappointing, I read somewhere about others logging support issues and being able to get device swapped out with one with bigger 64GB, so information on if this is an option would be great, as otherwise may have to look at getting slightly bigger model and migrating configs across but that would be a pain in the ***.

Yesterday we had an issue with our air-conditioner which caused the Palo Alto Firewall to restart due to high temperature. After the device booted up, I noticed some logs saying that disk is not detected/degraded. I tried restarting it one more time and the firewall still reports those logs. How can I fix this? Your advice/support is highly appreciated.

Btw, I'm trying to open a case for this issue, but cannot proceed at Step 3 (Select Asset). I don't see any button to choose an asset as suggested in this guideline: -Articles/How-to-Use-the-New-Web-Based-Case-Creation-...

But for the life of me, I cannot figure out how to add another disk (virtual hard drive) to my BIG-IQ VE. I don't want to expand the current disk... which is what I am finding all of the articles pertain to (and which I already know how to do). My desire is to add another HD (via HD2) to the VE.

So, what this means for deduplicated jobs is that an original job that protected all of the application data on a client was written to disk. Then subsequent jobs do not write this data again to the disk, which is the principle of deduplication only write data once.

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