**Describe the bug**

Since we upgraded to 20.10.3.30, one of our clickhouse cluster takes much more time to start. (Up to 50 minutes, and before it took ~3 minutes)
The log file is filled with
>  <Debug> DiskLocal: Reserving 1.00 MiB on disk `default`, having unreserved 16.90 TiB

Additionally, the memory consumption increases, linearly, a lot (up to arround 230 G for us) and then drop back to normal values once clickhouse finished starting up. During that loading phase, a single CPU core is used at 100%.
If that memory is not available for the machine, clickhouse gets OOMed by the kernel.


**How to reproduce**
* Issue appeared after we upgraded to ClickHouse server version 20.10.3.30

* How could I find wich of our tables may be responsible for that ?


**Expected behavior**
A fast startup :)

{
            /
            /
            /
            /
            /
            /
            
            /
            /
            /
            auto disk = moving_part.reserved_space->getDisk();
            if (supportsReplication() && disk->supportZeroCopyReplication() && settings->allow_remote_fs_zero_copy_replication)
            {
                /
                /
                /
                /
                if (auto lock = tryCreateZeroCopyExclusiveLock(moving_part.part->name, disk); lock)
                {
                    cloned_part = parts_mover.clonePart(moving_part);
                    parts_mover.swapClonedPart(cloned_part);
                }
                else
                {
                    /
                    LOG_DEBUG(log, "Move of part {} postponed, because zero copy mode enabled and someone other moving this part right now", moving_part.part->name);
                    result = false;
                    continue;
                }