Why *not* to use a SSD for Time Machine Backup
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When the drive is
full, the SSD needs to find out which blocks are partially filled, move
that information into a cache and then write it back to the drive. It is
best to have 10-15% of your drive set aside for free space, to keep a
good balance between performance and space utilization."Back in the day it was common to have a "defragmentation" tool for the harddrive, which would move all free space to a continuous segment. It should be pretty simple to do the same for an SSD, no?
@Klaus said in Why *not* to use a SSD for Time Machine Backup:
Back in the day it was common to have a "defragmentation" tool for the harddrive, which would move all free space to a continuous segment. It should be pretty simple to do the same for an SSD, no?
I would think so, but I also believe that SSDs are limited by the number of read/write cycles per block. Performance starts to suffer after a while.
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When the drive is
full, the SSD needs to find out which blocks are partially filled, move
that information into a cache and then write it back to the drive. It is
best to have 10-15% of your drive set aside for free space, to keep a
good balance between performance and space utilization."Back in the day it was common to have a "defragmentation" tool for the harddrive, which would move all free space to a continuous segment. It should be pretty simple to do the same for an SSD, no?
@Klaus said in Why *not* to use a SSD for Time Machine Backup:
Back in the day it was common to have a "defragmentation" tool for the harddrive, which would move all free space to a continuous segment. It should be pretty simple to do the same for an SSD, no?
It is already being done (to different degrees by different SSDs/systems), it’s called “garbage collection”:
https://datarecovery.com/rd/garbage-collection-ssd-simple-explanation/
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Re: the opening post … what I hope to see is performance comparison between filled SSD vs. HDD.
SSD can slow down after it is filled, but if after the slowdown it still outperforms the HDD, then it would still be worthwhile to use SSD.
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Re: the opening post … what I hope to see is performance comparison between filled SSD vs. HDD.
SSD can slow down after it is filled, but if after the slowdown it still outperforms the HDD, then it would still be worthwhile to use SSD.
@Axtremus said in Why *not* to use a SSD for Time Machine Backup:
Re: the opening post … what I hope to see is performance comparison between filled SSD vs. HDD.
SSD can slow down after it is filled, but if after the slowdown it still outperforms the HDD, then it would still be worthwhile to use SSD.
How many have you built, Ax?
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@Klaus said in Why *not* to use a SSD for Time Machine Backup:
Back in the day it was common to have a "defragmentation" tool for the harddrive, which would move all free space to a continuous segment. It should be pretty simple to do the same for an SSD, no?
It is already being done (to different degrees by different SSDs/systems), it’s called “garbage collection”:
https://datarecovery.com/rd/garbage-collection-ssd-simple-explanation/
@Axtremus said in [Why *not* to use a SSD for Time Machine
It is already being done (to different degrees by different SSDs/systems), it’s called “garbage collection”:
A terrible choice of name. Since the 1950s, the term "garbage collection" refers to a process of identifying blocks of memory that aren't needed anymore, either by tracing references start from a "root" set of references, or by a process called "reference counting". The "garbage collection" process of an SSD seems to not actually identify any garbage; rather, it seems to be only about compactifying and restructuring blocks.
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I recently replaced the HDD in a TimeCapsule with an SSD. It will be a while until that SSD fills up. I still have another TimeCapsule of the same model with an HDD. So if that HDD survives until the SSD fills up, I will have two systems that will let me compare their performances.
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Re: the opening post … what I hope to see is performance comparison between filled SSD vs. HDD.
SSD can slow down after it is filled, but if after the slowdown it still outperforms the HDD, then it would still be worthwhile to use SSD.
@Axtremus said in Why *not* to use a SSD for Time Machine Backup:
Re: the opening post … what I hope to see is performance comparison between filled SSD vs. HDD.
SSD can slow down after it is filled, but if after the slowdown it still outperforms the HDD, then it would still be worthwhile to use SSD.
This is only about write speeds, no? So I assume it would still outperform HDDs in read speed.
I think it's a little sad that "hybrid" drives that have a smaller SSD and a big HDD aren't more common. A clever file system could combine their respective advantages.
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@Axtremus said in [Why *not* to use a SSD for Time Machine
It is already being done (to different degrees by different SSDs/systems), it’s called “garbage collection”:
A terrible choice of name. Since the 1950s, the term "garbage collection" refers to a process of identifying blocks of memory that aren't needed anymore, either by tracing references start from a "root" set of references, or by a process called "reference counting". The "garbage collection" process of an SSD seems to not actually identify any garbage; rather, it seems to be only about compactifying and restructuring blocks.
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@Axtremus said in Why *not* to use a SSD for Time Machine Backup:
Re: the opening post … what I hope to see is performance comparison between filled SSD vs. HDD.
SSD can slow down after it is filled, but if after the slowdown it still outperforms the HDD, then it would still be worthwhile to use SSD.
This is only about write speeds, no? So I assume it would still outperform HDDs in read speed.
I think it's a little sad that "hybrid" drives that have a smaller SSD and a big HDD aren't more common. A clever file system could combine their respective advantages.
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Yes, mostly affect write speed, not so much on read speed
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Hybrid drive with smaller SSD + bigger HDD … for a while that’s the standard for iMacs. Even Apple stopped doing that now. I guess people just don’t want to deal with the mechanical failures of HDD’s moving parts. For a system that never shuts down (servers), I am guessing an HDD with very big cache will likely work as well or better than a hybrid SSD+HDD.
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Yes, mostly affect write speed, not so much on read speed
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Hybrid drive with smaller SSD + bigger HDD … for a while that’s the standard for iMacs. Even Apple stopped doing that now. I guess people just don’t want to deal with the mechanical failures of HDD’s moving parts. For a system that never shuts down (servers), I am guessing an HDD with very big cache will likely work as well or better than a hybrid SSD+HDD.
@Axtremus said in Why *not* to use a SSD for Time Machine Backup:
- Yes, mostly affect write speed, not so much on read speed
I would think that's not a major issue in backup, particularly if incremental, such as Time Machine.
- Hybrid drive with smaller SSD + bigger HDD … for a while that’s the standard for iMacs. Even Apple stopped doing that now. I guess people just don’t want to deal with the mechanical failures of HDD’s moving parts.
My 2014 iMac has such a drive. It failed after about 3 years. I had it replaced. But, I'm currently booting from an external SSD and it works great. My Time Machine backup is to a 4TB RDHD.
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