Hard Drive Space

Discussion in 'Buying Tips and Advice' started by BlueEyedSon, Jul 13, 2015.

  1. BlueEyedSon macrumors newbie

    Jun 14, 2015
    I'm in the market for a new laptop. I think the new Macbook will meet my needs, but I'm unsure about how big of a hard drive I'll need. In the past, I've purchased laptops with larger hard drives as I don't want to run out of space. I currently have about 125 gb on my hard drive and I keep everything on it. I've heard that it's a good idea to make sure that there is "ample" free space on a hard drive, not just to keep it from filling up too quickly, but to ensure that it runs most efficiently. How much free space is needed on a hard drive to keep it running quickly? Is it a specific amount of free space that's best (e.g., 10gb) or rather a percentage of the total capacity of the drive (e.g., 10%, so of a 256gb hard drive, ~25gb should be free)?
  2. throAU macrumors 603


    Feb 13, 2012
    Perth, Western Australia
    A rule of thumb i find helpful (and based on metrics suggested by enterprise storage arrays and ZFS) is to go no more than 80% full. The reason for a percentage is because as time moves on the chances are with bigger drives you'll be storing bigger files...

    The reasoning for this is that once you start getting towards that limit, as you delete and recreate files, the drive/filesystem has a hard time ensuring they are stored in contiguous blocks of space. Presumably, SSDs will also have a harder time performing wear-levelling with limited free space as well.

    Also - with a hard drive (this bit is not relevant with SSD) the outer tracks read/write faster than the inner tracks - they're on the outside edge of the disk and more data can be read per revolution. So hard drives do in fact get slower the closer you get to the end of the disk. Especially once you get past 50%. Keeping as much free space as possible (i.e., keeping your data as close to the outer tracks as possible) also limits the distance the read/write head has to move, which reduces seek times drastically. Which is a big win for spinning disks.


    Spinning hard disk: I'd suggest get double the space you need or more if you can afford it, to run on the faster outer tracks, limit the distance the read/write head has to move, and eliminate disk fragmentation problems. Hard disks are cheap now anyway.

    SSD: I'd try and stay under 80% full to avoid filesystem fragmentation and give the drive a better chance at doing wear levelling.
  3. Samuelsan2001 macrumors 604

    Oct 24, 2013
    Sounds like 256 will be fine for you especially if you go through and delete anything you don't need anymore. I always go with 20% for Hard drives as a good rule of thumb and 16Gb for SSD's just seems about right.
  4. tjwaido macrumors member

    Aug 24, 2008
    The wild west.
    Go for an SSD/Flash drive and max your memory to get the best performance. I just upgraded my sister's 2011 MacBook Pro that was running slow and eating up all her RAM. I installed a Transcend 1TB SSD and maxed out her memory with 16GB of ram from OWC. All her apps including Photos runs so efficiently now.
  5. Dark Void macrumors 68030

    Dark Void

    Jun 1, 2011
    I agree that a 256 GB should suffice. It's ample for what you have installed already, and leaves you plenty of space for expansion.
  6. ApfelKuchen macrumors 68040

    Aug 28, 2012
    Between the coasts
    Based on your current usage, I'd agree that 256 GB will probably be enough. "How much do I need?" always ties into "How much can I afford?" Since SSD is roughly four times the cost of HDD, cost becomes a larger factor in that decision.

    Traditionally, the rule of thumb has been, "the new computer's HDD should be double the current computer's HDD." This rule was developed back in the Dark Ages of MS DOS and the transition from MS DOS to Windows. Apps and OSes were getting larger, seemingly by the minute, as new functions and capabilities were being added. The situation has dramatically stabilized since then. If, over the course of 10 years or more, you've managed to accumulate 125 GB of OS, apps, and data, it's highly unlikely you'll accumulate another 125 GB over the course of the next 4-5 years. And if it happens that you do, there are any number of ways to manage the situation.

    So, if you budget 15% for overhead (split the difference on that 10-20% rule of thumb), On a 256 GB SSD, you'd have:

    125 GB for existing OS, apps, and data, 38.4 GB for overhead... 92.6 GB remains for new apps, data, etc. At Apple's current price for 200 GB of iCloud storage ($3.99/mo. - approx. $0.02/GB) and their current price for SSD ($250 for 256 GB - approx. $1.00/GB) - we're talking about a break-even point of about 4 years. So, does it make a lot of sense to buy a 512 GB SSD if chances are small that the extra 256 GB will actually be used?

    You can stop reading here if you wish, as everything that follows is simply rationalizations and observations...

    One of the reasons we get over-sized HDDs is that it simplifies our lives - it seems neat and convenient to have all our files in one place/on one drive, and if we have enough empty space, we may never have to spend time cleaning house. If we can't afford the luxury of "excessive" empty space, then perhaps we have to do a bit more work over the course of time.

    I'm not sure why SSD would need substantially less or more "headroom" (10-20% free space by most folks' rules of thumb) than HDDs. Part of that free space exists to ensure that there'll be room for caches, which shrink and grow based on the work you're doing. Caching requirements would be the same for HDD and SSD. Part of the headroom is there to help us avoid "disk full" issues while we're in the midst of a project, especially if we're working with large files. Again, no difference there between HDD and SSD.

    And part of the overhead is there to help avoid file fragmentation. There's plenty to be read about fragmentation if you search the web (don't pay attention to articles that discuss Windows, limit yourself to OS X, as the Mac HFS Plus file system is designed to minimize fragmentation). Even if fragmentation was a problem (which for the most part, it is not), SSDs eliminate much of the negative impact of fragmentation - unlike an HDD, there is no speed penalty paid when reading a fragmented file from an SSD.

    File fragmentation also goes contrary to some folks' notions of tidiness. All I can say to them is that our conventional notions of tidiness can be inefficient when applied to data storage. Why should it matter where a particular bit of a file happens to be, so long as the file system knows how to find it? Wouldn't it be absurd to think, "All memories of my parents should be stored in contiguous synapses, I have to rearrange things?"
  7. throAU, Jul 14, 2015
    Last edited: Jul 14, 2015

    throAU macrumors 603


    Feb 13, 2012
    Perth, Western Australia
    With small amounts of free space, fragmentation can definitely become a real problem. I've had a server with a GB or so of empty space on a drive before that could not actually write to disk because the filesystem was so fragmented that it couldn't actually split the file(s) up into enough fragments to fit. The space was empty but just way too scattered.

    With spinning disks it is even worse as if the file is not stored in contiguous space, several read/write head movements and several additional revolutions of the disk will be required to read it. This slows things down. A lot. The massive amounts of suggested free space for spinning disks (50-80% unused if you can afford it, but spinning disk is cheap now) is all about speed. you're attempting to limit the distance the read/write head has to move to access anything you have on the disk in order to speed it up (a full inside to outside sweep may be say 10ms, if you can limit the used area to the first 50% you've cut your average head seek time in half). Plus: the outer tracks on the start of the disk are roughly 2x the speed of the inner tracks at the end of the disk for sequential reads.

    On SSD that part isn't a problem, but the first point above is a filesystem issue (lack of ability to write at all due to excessive fragmentation) and will happen irrespective of the media used.

    Short-stroking and other hard drive tuning tricks are going to die out real soon though because SSD is getting cheap enough.
  8. BlueEyedSon thread starter macrumors newbie

    Jun 14, 2015
    Thanks for the helpful advice! I think I still use the term "hard drive" generically and I definitely intended to include solid state drives in my question as that's what I'd be getting with a new macbook. As apfelkuchen surmised, it has, indeed, been about 10 years over which I've accumulated the current stuff on my hard drive and I've not been attempting to save space, which I'm sure I could. So, it really sounds like a 256 gb drive will provide ample space for me over the next several years without having to worry. Thanks!!!
  9. coachingguy macrumors 6502a


    Feb 7, 2003
    The Great White, Albeit Frozen North
    I've got a late 2012 Macbook Pro w/ the 500 gb standard 5400 rpm drive... With all my pictures (amateur/sorta semi-pro photog) and music plus real world stuff, I've been struggling to even keep 20gigs of Free space... Which as you can guess can have a detrimental effect on performance...

    I just recently decided to upgrade my HD... I decided to get a 1tb internal drive. Since the cost of an SSD in that size is more than the value of the laptop... I choose the HGST 1 tb, 7200 rpm, 32mb cache for $65... I'll get it tomorrow, get it installed and cloned and, while I know it's not SSD, I'm still expecting a significant performance boost because of all the extra space.

    The comment about the more space you have, the more "stuff" you fill it with a and the increasing size of everyday files... Too true.


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8 July 13, 2015