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#9770 - 05/04/10 06:40 PM TimeMachine:One backup drive outperforms the other
JoBoy Offline


Registered: 08/05/09
Are there any ideas why one backup drive is outperforming the other by such a wide margin?

I routinely use two 1TB hard drives to store Time Machine backups. One is an internal Hitachi 1TB hard drive I bought from Apple and the other is a 1TB OWC Mercury Elite 1TB external FW800 hard drive from OWC. My main hard drive is a 1TB Hitachi internal drive that I bought from OWC. During the day, I change the backup destination drive by using the Select Disk option on TM preferences. At the end of the day, both backup disks have up-to-the-minute TM backups.

Over time, I noticed that the number of days between the oldest TM backup and the date of observation was much larger for the internal Hitachi from Apple. I then recorded 10 observations between April 7, 2010 to May 4, 2010. During that time, the OWC external drive's number of days varied from 2 to 9 days (average 5.9 days) while the internal Hitachi drive's number of days varied from 11 to 25 days (average 17.8 days). The average number of days for the internal Hitachi were 3 times more than for the OWC external drive.

Disk Utility shows that both backup drives have the same capacity. The OWC drive's used space varies from 595GB to 922GB but for the other 8 observations, it was in the mid 700 to upper 800 GB range. The internal Hitachi's used space was consistently in the low 900GB range.

Other info that may be useful: The main hard drive routinely has used space of 270GB, plus or minus a few GBs depending on what has been added and deleted. The largest item to be backed up is a VMware virtual machine that contains Windows 7 Ultimate. It weighs in at 160GB including all Windows apps & data (that's 59% of the main hard drive's used space).

Any suggestion as to how I can improve the performance of the OWC Mercury Elite?
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Mac Pro dual Quad-Core Intel Xeons Early 2008; 16GB RAM; MacOS X 10.11.6, iOS 9.3.5

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#9771 - 05/04/10 07:11 PM Re: TimeMachine:One backup drive outperforms the o [Re: JoBoy]
joemikeb Online

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Registered: 08/04/09
Loc: Fort Worth, Texas
How are you using two Time Machine Drives? My system only allows me to select one drive for TM use.
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#9774 - 05/04/10 07:59 PM Re: TimeMachine:One backup drive outperforms the o [Re: joemikeb]
JoBoy Offline


Registered: 08/05/09
It's true that you can only use one drive at any given moment, but you can change the target drive any time you want. Just go to Select Disk on Time Machine preferences and choose the second backup disk. Time Machine will then bring the newly selected disk up to date. Then use preferences to select the original backup disk and Time Machine will bring that one up to date. I change disks manually because I don't know how to do an AppleScript to make the changes automatic. This gives me two copies--one internal and one external.

I don't know of any drawbacks associated with this practice, but maybe the problem I'm asking about is a red flag pointing to a problem of which I'm not aware. Logically, I don't see why this can't be done.
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#9781 - 05/05/10 09:36 AM Re: TimeMachine:One backup drive outperforms the o [Re: JoBoy]
joemikeb Online

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Registered: 08/04/09
Loc: Fort Worth, Texas
It can be done, but at the end of the day only one of the drives will have an up to date backup because the other's hourly backups ended when you switched drives. That also mean the drives will have different cycles for merging the daily backups into the weekly backups and weekly backups into the monthly. So you are comparing apples and oranges (or is that Apples to PCs)? smile

A better plan for you might be to use one drive for Time Machine all the time and then use something like SuperDuper to clone your main drive to your other backup drive. If you want to backup multiple machines to the "clone" drive or to have a bootable image on the "clone", SuperDuper can clone to a device image (dmg) file.
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#9789 - 05/05/10 04:45 PM Re: TimeMachine:One backup drive outperforms the o [Re: JoBoy]
Virtual1 Offline


Registered: 08/04/09
Loc: Iowa
I have an OWC Elite-AL Pro ext fw800 and it screams, I have no problem maxing the firewire connection at 85MB/sec.

Internal drive should do better, the WD drive I have in my AL-Pro tops out at 86MB/sec or so which is very close to the firewire limit, so it performs nearly identically when installed in the mac pro internally.

Network connections, particularly wireless, will go slower. As will USB, particularly on PPC.

You can use DD to test drive access speeds. Just be careful, you can wipe a drive pretty quick with the wrong command. wink

It never ceases to amaze me the difference in drive speeds. The drive above that does 83MB/sec in the OWC enclosure was removed from the WD case (green drive) it came in, which did between 8 and 14 MB/sec over usb..... wow.
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#9793 - 05/05/10 10:11 PM Re: TimeMachine:One backup drive outperforms the o [Re: joemikeb]
JoBoy Offline


Registered: 08/05/09
Originally Posted By: joemikeb
It can be done, but at the end of the day only one of the drives will have an up to date backup because the other's hourly backups ended when you switched drives...


That's not so because just before I shut down I make sure that both drives have a backup that is current as of the end of the day. I just use the Select Disk and perform a backup on each drive.

It's true that the hourly backups are not the same, but one disk or the other will have what I want. If I'm hunting for a particular hour (which I've never felt the need to do) I can find it. If there's been a catastrophic main hard drive failure (I had two about 5 months ago), I can get a new drive and then restore the whole system, apps, documents and settings from the most current backup on either backup drive using the Snow Leopard install disk. That restore feature lets me choose which TM backup drive I want to use. That's where I got the idea of dual TM backup drives.

I never get to a weekly or monthly backup. It's just hourly for a day and then daily. I think I'll have to get a 2TB hard drive to get the weekly and monthly. The daily backups are erased before they ever have a chance to be converted to a monthly.

I've used SuperDuper! for about 3 years. I had problems when I had a bootable clone on another internal hard drive in addition to the main hard drive. The main drive and the clone on the internal backup drive acted as though they were communicating. I worked on it, but was not able to figure out how to fix it. I would get unexpected strange things such as duplicate appointments on the Palm Desktop when I would synchronize with my Palm Centro. Finally, I deleted SuperDuper! and used Time Machine exclusively. That cured the problem and I've been living happily since then. If I just had SD! on an external drive that is turned on just to make a clone and then turned off or disconnected, I wonder whether that, too, would have cured my problem, but I'm really happy with TM and its ability to restore files or folders from TM without using the install disk and a to restore the whole system,apps, and documents and settings by using the install disk.

This brings me back to my original question as to whether or not I can coax the external drive to keep more data before deleting. The external typically stores only 700 to upper 800GB range before deleting files while the internal drive consistently stores data from the same source in the low 900GB range. I usually use the external drive most of the time and just switch over to update the internal drive when I think of it and then immediately switch back to the external drive. I feel like the external drive is wasting anywhere from 50GB to 150GB depending on when it chooses to erase and how much.
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Mac Pro dual Quad-Core Intel Xeons Early 2008; 16GB RAM; MacOS X 10.11.6, iOS 9.3.5

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#9861 - 05/10/10 03:29 PM Re: TimeMachine:One backup drive outperforms the o [Re: joemikeb]
ganbustein Offline


Registered: 08/04/09
Originally Posted By: joemikeb
It can be done, but at the end of the day only one of the drives will have an up to date backup because the other's hourly backups ended when you switched drives. That also mean the drives will have different cycles for merging the daily backups into the weekly backups and weekly backups into the monthly.

There's a common misconception buried in that statement. TM never merges backups. The first hourly backup on any given day eventually becomes that day's daily backup. A daily backup becomes a weekly backup when it's at least 30 days old and at least 7 days younger than the previously youngest weekly backup. In each case, the intermediate backups, the ones that didn't get promoted to the next level, are simply deleted. There's no merging going on.

Any given file will typically be a member of several backups, all of which share a single physical copy of that file. That single copy gets deleted when the last backup it's a member of gets deleted. The use of the word "last" (rather than "first") in that sentence is the closest approximation to any sense of the word "merge" in connection with Time Machine.


Nevertheless, your point about the two backups having different cycles is valid. At the time TM is thinning old backups, one backup volume will have more hourly backups than the other. That volume thereby has less space available for daily backups, and has to reap them more aggressively.

If the backup volumes are filling up as quickly as the OP suggests, there must be some large frequently changing files getting backed up, so those hourly backups will have a lot of unique files taking up a significant amount of space. That makes the number of hourly backups a significant factor.

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#9863 - 05/10/10 04:57 PM Re: TimeMachine:One backup drive outperforms the o [Re: ganbustein]
JoBoy Offline


Registered: 08/05/09
Originally Posted By: ganbustein
If the backup volumes are filling up as quickly as the OP suggests, there must be some large frequently changing files getting backed up, so those hourly backups will have a lot of unique files taking up a significant amount of space. That makes the number of hourly backups a significant factor.


That's true. I use VMware Fusion 3 to run Windows 7 Ultimate on my Mac. Its virtual machine was in a single file 160GB in size, but I've found a way to trim it down to 20GB by not allocating unused space. I'm a newbie with VMware and it's not easy to figure out the nuances of efficient use. I'll be able to go a long time without getting back to the huge size.

Thanks to joemikeb and you, I've come to understand a lot more about Time Machine. It's really a sold performer. I just have to learn the ropes.


Edited by JoBoy (05/10/10 04:59 PM)
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#9880 - 05/11/10 10:43 AM Re: TimeMachine:One backup drive outperforms the o [Re: JoBoy]
joemikeb Online

Moderator

Registered: 08/04/09
Loc: Fort Worth, Texas
Parallels Desktop will exclude the virtual machines from Time Machine backups because any time you open a virtual machine there are changes and therefore TM will make yet another copy full copy of this rather large file on the TM drive. Frankly I would be a bit surprised if VM Fusion doesn't offer the same option but in general it is recommended to exclude virtual machine files from Time Machine backups. Even if VM Fusion doesn't offer the option it is easy enough to do in System Preferences > Time Machine > Options.
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#9883 - 05/11/10 12:25 PM Re: TimeMachine:One backup drive outperforms the o [Re: joemikeb]
JoBoy Offline


Registered: 08/05/09
Thanks for the suggestion. I do use the TM exclusion feature to exclude backing up from a Photoshop scratch volume, from Time Machine disks, and from another internal drive that I use for miscellaneous purposes. After reading your suggestions, I took another look at VMware Fusion's features and found that it has a feature that allows me to allocate a maximum size for the virtual machine and then have the machine only expand in 2GB increments as needed so as not to waste disk space with an unneeded, fixed disk size. I initially didn't understand that option and had 160GB reserved in one big chunk for VMware/Windows 7. Activating that option reduced the VMware virtual machine size from 160GB to 20GB, saving my self 140GB of wasted space. I'm continuing to back up VMware along with the rest of my system, apps, and documents because I've experimented with restoring the whole system from Time Machine to an extra internal drive and it works beautifully. It's just like any other file. VMware with Windows 7 doesn't miss a beat after being restored from TM. That way, I don't have to worry about about special handling and backups for Windows 7. My initial post on this thread was provoked by the negative effect that the extra 140GB of empty space was having on TM backups. Now that I've eliminated that humongous file, things are humming along much better. You've been a great sounding board and you got me thinking about what I could do to improve things. I really appreciate it. smile
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